Why Your Estimates Are Always Wrong (And How to Fix Them) Developers underestimate completion time by 50%. Not because they are incompetent. Because of a cognitive bias called the planning fallacy. What Is the Planning Fallacy? In 1994, Buehler, Griffin, and Ross published a landmark study in the Journal of Personality and Social Psychology. They found that people systematically underestimate how long tasks will take — even when they have relevant past data. The mechanism: we plan for best-case scenarios and ignore obstacle likelihood. Our internal simulations are rosier than reality. The Research Buehler et al. asked students to estimate when they would complete their senior theses. The median prediction was 33.9 days. The actual median completion: 55.5 days. Only 30% finished by their predicted date. The other 70% were late — some by weeks. Even more striking: when asked to estimate completion dates for "similar students," predictions were more accurate.…