> But they don't. Nobody does. They don't just get the timelines wrong, they get the tasks and milestones wrong - which makes sense, because the people asking for the estimates don't actually know what the goals are, usually even after the software is delivered.

I definitely agree that the people asking don't actually know what the goals are. They usually have a very fuzzy picture there.

But I've always found the estimation and planning process to be hugely valuable for revealing the questions that reveal to THEM that they don't know all those requirements yet. And then we have a discussion about them, and we get better specs as a result, and then go on from there... which is way better than when we don't discover those gaps until we are writing the code for it!