IMO if you're familiar with the language and libraries it's pretty easy to predict how long writing some feature will take (provided there aren't bugs in anythi

IMO if you're familiar with the language and libraries it's pretty easy to predict how long writing some feature will take (provided there aren't bugs in anything you're working with, you don't get any weird emotional hangups etc. Those are fairly rare.) What's hard to predict (at least for me) is writing non trivial config files or using some new library or language or finding a new algorithm. Some of those things you might be able to estimate how long it might take to estimate the time it will take but other times you just have to say "I don't know" and time box it.