Combatting the planning fallacy

1. If you know how long things have taken in the past, use that data
2. if you don't know that then apply a heuristic so that you end up in a place so pessimistic, you are 50% likely to take less time than the estimate
   1. One deeply simple heuristic: be as pessimistic as you can reasonably manage, then double it
3. Try to decompose something big into it's parts (we tend not to do that automatically leading to course grain and bad estimates)
   1. While doing this, you should account for T_unknown, the subtasks you anticipate (the idiom "once you do 90% you only have the second 90% left" applies)
   2. Then apply your favorite heuristic from #2
4. You should also discount how much of an improvement you think something will be (we overestimate the benefit while underestimating the cost
5. Time boxing (useful because part of planning fallacy is Parkinson's Law)