Right on. I've been in web-dev for about fifteen years, and most of it is great fun, but ... my least favourite part is estimating project completion times. I'll keep this jigsaw analogy in mind the next time I have to explain these things to non-techies. I'll ask them how long they think it'd take to complete a million-piece jigsaw, but the piece count changes every time you count them, and some pieces keep merging, others split, some disappear, others pop into existence, various regions of the puzzle decide it'd be great fun to begin conquering the third dimension, on and on and on. The only way to be completely accurate with time estimates is to hold not only every bit of code in your head all at once, but understand how every bit interacts with every other bit, and also how every combo of bits interacts with the wider world. It's impossible. No-one can do it. Time estimates are always wrong and always too low. I hate them. Love the job, hate the estimation.