Assumptions Are the New Requirements—Declare Them, Then Test Relentlessly

Many teams kick off with a mountain of documented requirements—features, flows, specs—assuming these will guarantee success. Yet, time and again, projects fail because the foundational beliefs weren’t true. Lean UX challenges this habit by asking teams to see every requirement as an untested assumption. Instead of accepting statements like 'users need an advanced reporting dashboard,' the method insists you first ask, 'Have we proven that users will use or value this feature?'

You’ll often be surprised when you distill your requirements into assumptions. Maybe you believe your target audience won’t mind a lengthy signup process, or that customers crave detailed analytics. Only when you pose these as hypotheses and test them with real people (even with a scrappy, partial version) will the truth emerge. Perhaps your users don’t even see analytics as valuable, or are willing to abandon your product at the first sign of friction.

Teams that learn to do this—write down their assumptions, make them public, then build quick experiments to prove or disprove—move faster and waste dramatically less time on dead ends. It’s a shift in mindset from certainty to curiosity, and from building to learning.

This principle reflects the scientific method: a cycle of propose, test, observe, and adapt. If you find yourself stuck in endless debate or reluctant to change direction, you’re likely mistaking assumptions for facts. Lean UX makes it safe—and normal—to question everything before scaling.

Try this with your next idea: jot down your strongest beliefs and assumptions about your audience and what will work. Choose the one with the biggest risk or uncertainty, and restate it as a hypothesis. Instead of building the full solution, craft a cheap, quick test or prototype—maybe just a clickable mockup, a fake button, or a short email campaign. Let real feedback, not opinions or documents, guide your next move—trust that every experiment, even if it fails, brings you closer to what actually works. See what happens when you test your assumptions before betting big.