Roadmaps fail on missing steps, not bad estimates — hunt the precondition early
A 60-engineer SaaS company hit every estimate yet shipped seven months late: its identity vendor wouldn't sign a regional agreement inside 90 days, killing the deadline in January without anyone noticing. Estimation error is bounded and can be buffered; a missing step can only add time. Work backwards from what must be true before execution, and get that answer before you schedule it. The fix is planning what isn't on the list yet.