&gt;  don&#x27;t let you even look at the problem space first<p>this is the core of the issue. when one has the time to break down all unknowns and discover them, estimate are quite spot on. but who want to pay for the estimate?<p>so we are left trying to guess what time a particular unknown is going to take to solve.<p>the good metaphor here is asking how much time it will take to solve a puzzle magazine, from cover to cover by looking at the title.