Friction resists motion; viscosity is resistance to flow. In physics, friction opposes relative motion between surfaces; viscosity is the internal resistance of a fluid to deformation. Both make change harder and costlier. The same idea applies to organisations, markets, and behaviour: things that should move often don't, or move slowly, because something is resisting. The model helps you find and reduce the resistance — or, when you want stability, add it deliberately.
Friction shows up as switching costs, approval layers, and habit. Customers don't switch because the effort of moving is high. Projects stall because every step meets resistance. Viscosity shows up as slow flow: information that doesn't spread, decisions that don't propagate, or change that oozes instead of runs. High-viscosity organisations need more force (pressure, leadership, crisis) to achieve the same flow. The strategic question is whether you want to reduce friction and viscosity (faster change, easier switching) or increase them (stickier customers, more stable processes). Usually you want less internal friction and more friction for competitors trying to take your customers.
Startups often win by reducing friction in a high-friction industry — one-click ordering, instant approval, no paperwork. Incumbents sometimes rely on friction as a moat: complexity and switching costs keep customers in place. The model is neutral: friction can be friend or foe depending on where it sits. Map where resistance is, who benefits from it, and whether you should be lowering or raising it.
Section 2
How to See It
Friction and viscosity show up when expected motion or flow is slow or blocked. Look for resistance to change, slow propagation of information or decisions, and costs that make switching or moving harder.
Business
You're seeing Friction & Viscosity when a sales process has many steps and approvals — each step is friction. Deals move slowly; some die in the pipeline. When a company "reduces friction" in the funnel, it is removing resistance so that the same effort produces more flow. High-friction competitors lose to low-friction alternatives.
Technology
You're seeing Friction & Viscosity when onboarding is long, integration is painful, or the product requires many steps to value. Friction is every click, form, and wait that stands between the user and the outcome. Low-friction products win when the job is the same; viscosity in the form of slow APIs or heavy processes makes adoption and iteration harder.
Investing
You're seeing Friction & Viscosity when capital or information flows slowly through a market. High transaction costs, illiquidity, and opacity are friction. The same asset in a low-friction market would reprice faster. Viscosity in organisational decision-making can delay a portfolio company's response to market changes — a due diligence topic.
Markets
You're seeing Friction & Viscosity when customers stay with an incumbent despite a better alternative. Switching costs — time, learning, contract, integration — are friction. The incumbent's moat is often friction that they have built or inherited. Disruptors often win by offering the same outcome with less friction (e.g. digital vs physical).
Section 3
How to Use It
Decision filter
"When progress is slow or flow is blocked, ask: where is the friction? What is the viscosity? Map the resistance. Then decide: do we want to reduce it (faster change, easier flow) or increase it (stickier customers, more stable state)? Usually reduce internal friction; sometimes increase friction for competitors."
As a founder
Reduce friction in the customer journey and in internal operations. Every unnecessary step, form, and approval is friction. Strip it. At the same time, build friction for churn — switching costs, integration depth, habit — so that leaving is harder. The best companies are low-friction to adopt and high-friction to leave. Audit your funnel and org for viscosity: where does information or decisions get stuck? Fix the bottlenecks.
As an investor
Assess portfolio companies for friction and viscosity. High internal friction means slow execution and poor responsiveness. High customer-side friction to adoption means slow growth unless you fix the funnel. High friction to churn (switching costs) is a moat. Ask where the resistance is and whether the company is deliberately designing for the right balance.
As a decision-maker
When change is slow, identify the source of resistance. Is it process (approval layers, committees)? Incentive (people lose from change)? Habit (we've always done it this way)? Each is a form of friction. Reducing friction may require changing process, aligning incentives, or creating a forcing function. Don't assume more pressure alone will work if the friction is structural.
Common misapplication: Treating all friction as bad. Friction can be desirable: it can protect quality, prevent bad decisions, or create switching costs that defend your position. The goal is not zero friction but the right friction in the right place. Reduce friction where you want flow; add it where you want stability or stickiness.
Second misapplication: Confusing friction with incapability. Sometimes things don't move because the system lacks capacity or skill, not because of resistance. Friction is resistance to motion that would otherwise occur; if the system cannot do the thing at all, the fix is capability, not friction reduction.
Bezos obsessed over reducing friction for customers — one-click ordering, fast delivery, easy returns. Amazon's growth was partly a story of systematically lowering the friction of buying. Internally, he pushed for single-threaded ownership and minimal process to reduce organisational viscosity. The strategic principle: make it easy to say yes (low friction to adopt) and, where possible, create friction for competitors (e.g. scale and logistics as a moat).
Jobs reduced friction in product use — fewer buttons, simpler flows, "it just works." Apple's design philosophy was to remove steps and cognitive load. The result was products that had lower friction to value than competitors. He also created friction for leaving the ecosystem (integration, lock-in), so that once in, customers stayed. Friction as strategy: low to enter, high to exit.
Section 6
Visual Explanation
Friction & Viscosity — Resistance to motion and flow. Low friction: fast change, easy flow. High friction: slow change, sticky state. Reduce internal friction; design friction for churn and competition.
Section 7
Connected Models
Friction and viscosity connect to inertia, activation energy, and flow. The models below either describe related resistance (inertia, activation energy), identify bottlenecks (bottlenecks, process overhead), or describe systems that depend on overcoming resistance (flywheel, switching costs).
Reinforces
[Inertia](/mental-models/inertia)
Inertia is resistance to change in state of motion — a body at rest stays at rest. Friction is what opposes the motion once you try to move it. Together they explain why change is hard: you must overcome both inertia (getting started) and friction (sustaining motion). Organisational inertia is often compounded by friction in process and incentive.
Reinforces
Activation Energy
Activation energy is the minimum energy required to start a reaction. It is the "hump" that must be overcome. Friction is the ongoing resistance once motion has started. Both concepts explain why some changes don't happen or don't spread: the initial push (activation) or the sustaining force (overcoming friction) is insufficient.
Leads-to
Bottlenecks
A bottleneck is a point where flow is constrained. High viscosity or localised friction creates bottlenecks — the narrow pipe, the approval step, the single point of dependency. Reducing friction at the bottleneck increases overall flow; the model helps you find where the resistance is concentrated.
Leads-to
Process Overhead
Process overhead is the cost of coordination, approval, and compliance. It is organisational friction: every meeting, form, and review is resistance to direct action. Reducing process overhead is reducing friction so that effort converts to output more efficiently.
Section 8
One Key Quote
"Focus on what won't change: customers will always want low prices, fast delivery, and vast selection. We work backward from that and remove everything that gets in the way."
— Jeff Bezos (paraphrased)
Removing what gets in the way is friction reduction. Bezos applied it to the customer experience and to internal operations. The principle: identify the desired outcome (motion, flow) and systematically reduce the resistance to it.
Section 9
Analyst's Take
Faster Than Normal — Editorial View
Map the friction. When progress is slow or flow is blocked, list every step, approval, and cost. Each is a source of resistance. Prioritise the highest-impact friction — the step that kills the most deals, the approval that delays the most decisions — and remove or simplify it first.
Asymmetric friction. You want low friction for adoption and high friction for churn. Design the customer journey so that saying yes is easy (few steps, clear value) and leaving is hard (integration, data, habit). The same applies to talent: easy to join, hard to leave for the wrong reasons (e.g. culture, growth).
Viscosity in orgs. Information and decisions that don't flow create viscosity. Too many layers, unclear ownership, and misaligned incentives make the organisation thick. The fix is often structural — flatten, clarify, align — not just "communicate more." Communication in a high-viscosity org still flows slowly.
Friction as moat. Incumbents often rely on friction: complexity, relationships, switching costs. Disruptors win by offering the same outcome with less friction. When evaluating competitive position, ask who has built friction in whose favour and whether that friction is durable or can be bypassed.
Section 10
Summary
Friction resists motion; viscosity resists flow. In strategy, both make change slower and costlier. Map where resistance is, reduce internal friction and friction to adoption, and add friction for churn and competitor entry. The best systems are low-friction to enter and high-friction to leave.
Ries on reducing friction in the build-measure-learn loop. Faster iteration is lower friction between hypothesis and test; minimum viable product is the least-friction version to learn.
The Heaths on change: direct the rider, motivate the elephant, shape the path. Shaping the path is friction reduction — make the desired behaviour easier.
Stocks and flows, feedback loops. Friction and viscosity appear as resistance in flow; the book provides tools for mapping and intervening in such systems.
Case study in systematic friction reduction in e-commerce. One-click, Prime, and logistics as a strategy of removing resistance to purchase.
Reinforces
Switching Costs
Switching costs are the friction that prevents a customer or employee from moving to an alternative. They are deliberately designed friction — you want high switching costs for your customers (so they stay) and low switching costs to adopt your product (so they come). The model frames switching costs as strategic friction.
Tension
[Flywheel](/mental-models/flywheel)
A flywheel gains momentum once spinning; the initial push overcomes inertia and friction. Once the flywheel is turning, friction still exists but the stored energy keeps it going. The tension: building a flywheel requires reducing friction enough that the initial push can get it started; too much friction and the flywheel never spins.
