I think the problem is that developers(including myself) tend to make estimates assuming that they're not going to find anything that makes them say WTF! Code i

I think the problem is that developers(including myself) tend to make estimates assuming that they're not going to find anything that makes them say WTF! Code is never perfect and it's extremely difficult to know how much time it's going to take to dissect and restructure code to accommodate your new feature.