alt Hacker NewsEstimates are difficult, but if you monitor your estimate vs actual, and then adjust your next estimate accordingly, then it becomes easier to have decent estimates.
There is also the adage that if you are late, then 100% of the time the customer will be unhappy, but if you are early, then 100% of the time the customer will be pleased.
So make people more pleased :-)
So always over estimate a bit (25%)
This only works when the next thing is reasonably similar to the last thing. In my 40 years doing this it's happened exactly once.