There's also feature creep, which is a pretty big problem in a lot of less organised companies and organisations. The original design may well be a six page we

There's also feature creep, which is a pretty big problem in a lot of less organised companies and organisations. The original design may well be a six page website with mostly static content, but the final version could just as easily be a web app with a built in help/support/ticket/chat system, member accounts and live updating from a third party API. One two week estimate easily becomes a six months one. Or it's delayed because of more and more edge cases being found and someone not wanting to be consistent about them. If the first, third, ninth, sixty second and hundredth items in a loop have to all act differently for seemingly random reasons, that adds a lot of time to the development. It unfortunately doesn't matter how good your estimate is if the company/client tosses out the orignal spec at the first possible opportunity. But for well managed projects, yeah, it's a good writeup.