Unfortunately, the only heuristic that works when it comes to software complexity is experience. And even that doesn’t work all the time. As a programmer I know I can use my prior experience building similar things to estimate how long each feature will take to implement. Then I add all that up and come up with a rough estimate of when I’ll be done with the project. But the fact of the matter is that in every project there are two or three bottlenecks that crop up during development. These bottlenecks suck up an inordinate amount of programmer time that can’t be reliably predicted beforehand. And so it throws your entire project off schedule by weeks or months.
That’s what someone without experience misses when they try to estimate complexity. They don’t realize that what works in almost any other situation, doesn’t work at all when it comes to software. And so next time you hear “I’m sure this will only take you a few days to code” try not to be annoyed with whoever said it. Just take a deep breath, link them to this post and go on with your day.
— Dan Shipper, I'm Sure It Will Only Take You A Few Days To Code
