agile

One of the hardest thing in software development happens already before any code is being written. Estimating how much development time some feature might take is, at it's best, a guesswork.

No matter how generous estimates are being made they are still almost always too optimistic. Even after the original developers estimate is doubled. Twice. On the other hand, on those rare occasions when the estimates are being beat they are being beated big time. In a longer project these are almost enough to compensate all the underestimates.