People consistently underestimate how long tasks will take — even when they have direct experience of similar tasks running over. The imagined best-case scenario displaces the evidence of actual past experience. In UX, this bias determines when users abandon flows, how they respond to time claims in onboarding copy, and how they experience discovering steps they did not anticipate.
In 1979, Daniel Kahneman and Amos Tversky described a consistent pattern: when people plan a task, they imagine an uninterrupted, best-case execution of it, and base their time estimate on that scenario. They do not ask how long equivalent tasks have actually taken in the past. The estimate describes an ideal. The experience delivers reality.
Kahneman later framed this as the difference between the inside view and the outside view. The inside view is what planners instinctively use: imagine this specific task, construct a plausible scenario of completion, derive an estimate. The outside view asks: what has actually happened to users who attempted this task before? The outside view produces more accurate predictions every time. It is almost never used.
For UX designers, the planning fallacy operates on both sides of the screen. Users apply it to every flow they enter — “this signup will take a minute” — and abandon when reality exceeds the estimate. Designers apply it to every flow they build — imagining an ideal user who reads every instruction and completes in one sitting. The gap between the imagined user and the real one is where most onboarding abandonment lives.
“Plans are best-case scenarios. The outside view asks: what actually happened to users who attempted this task before?”
— Daniel Kahneman, Thinking, Fast and Slow, 2011
“Get started in 2 minutes” is derived from the inside view: a designer imagining a user who reads clearly, has everything at hand, makes no errors. The observed user takes considerably longer. When the gap between the promise and the experience is felt, it is attributed to the product.
Maze's 2023 product onboarding benchmark found that products with inaccurate time claims had 23% higher early drop-off than those with accurate estimates. Both phones below show the same six-step flow.
Tap “Get started.” A timer tracks elapsed time. Notice when it exceeds the 2-minute promise.
Time claim based on actual sessions. The “You'll need” list lets users check readiness.
The accurate estimate does not reduce signups. Users who proceed after seeing an honest time estimate complete onboarding at higher rates — because they opted in with accurate expectations rather than discovering mid-flow that the task was longer than anticipated.
When a user enters a multi-step flow without knowing its total length, they apply the planning fallacy immediately: they form an implicit estimate based on the first step. When that estimate is wrong, each unexpected step is experienced as a violation. Nielsen Norman Group found that users who knew total step count upfront had 31% higher completion rates.
Click “Next” repeatedly. Notice when it feels like it should have ended.
Total scope shown from step one. Each step is expected, not a surprise.
When the total is visible from step 1, users make a commitment to the full scope. When steps are hidden, step 4 is a surprise, and every surprise step is experienced as a planning fallacy violation: the task is more than anticipated, and the product is responsible.
The planning fallacy's most damaging UX manifestation is the mid-flow blocker: a required field that asks for information the user does not have at hand. API keys, VAT numbers, bank routing codes — these are outside the user's inside view of the task. Baymard Institute identified “required to look up information” as the second most common reason for checkout abandonment.
sk_live_⚠ You'll need to log into your Stripe account to find this
User is at step 4 of 6. The API key was not in their inside view. Most users close the tab.
Prerequisites surfaced upfront. Click the checkboxes to confirm readiness.
The prerequisite screen does not add friction — it relocates it. The effort of finding the Stripe API key is the same whether encountered mid-flow or before. The difference is that mid-flow, it is experienced as a violation against an existing investment. Before the flow, it is part of the upfront scope.
Kahneman, D., & Tversky, A. (1979). Intuitive prediction: Biases and corrective procedures. TIMS Studies in Management Science, 12, 313–327. · Lovallo, D., & Kahneman, D. (2003). Delusions of success. Harvard Business Review, 81(7), 56–63. · Maze (2023). Product Benchmarks: Onboarding. · Baymard Institute (2022). Checkout Usability: Why Users Abandon.