How Assumptions Sneak Into Strategy and Undermine Even Great Plans

The biggest trap for even the smartest planners isn’t lack of effort—it’s assuming that what “everyone knows” is actually true. Teams rush to fix problems and chase new opportunities, basing choices on a string of beliefs often left unstated and untested. That’s how a nonprofit invests in an elaborate online donation system, only to discover later that their audience prefers mailed checks. It’s how product teams blame each other when unexpected hiccups derail timelines—each group unknowingly betting on different, unspoken ‘truths.’

Here’s a micro-story: At a local café, a manager orders a month’s supply of oat milk, assuming vegan lattes will stay hot sellers. He’s shocked when half the cartons expire untouched, soon realizing a competitor’s new seasonal menu lured loyal customers away. His “everyone wants plant-based” belief was out of date, but nobody had asked regulars what they’d try next.

Psychologists call this confirmation bias—our brains’ tendency to notice only what fits our views and ignore contrary evidence. The real skill isn’t having the 'right' hunches, but systematically hunting down hidden assumptions and poking holes in them. Until you map, check, and prioritize these big bets, you’re flying blind. Sometimes finding out you were wrong stings, but it leaves you stronger, if you’re willing to course-correct.

Start by jotting down every key assumption you’re making about your plan or project, even if it feels silly to write out. Then, bring in outside eyes—ask your team, your customers, or experts to poke holes at your list. Don’t play defense; treat every challenge as a goldmine. Pick your riskiest, least-certain beliefs and set up a quick check—a call, survey, sample, or data search. Even a small test is better than betting on a guess, and it could save you months of headaches. Try it out before your next big move.