[firewolf34]

Requirements set constraints which guide the development process. Without them set early on, you risk not understanding completely what you're setting out to do, you risk differing expectations/assumptions between members of your team, and you risk creep as the project goes on which means you will diverge from your intended outcome.

In any project, resources (time, money, etc) are limited so the most successful project will be one that uses resources most efficiently. So good explicit requirements allow you to determine the most efficient manner to achieve them as they codeify the problem and give you goalposts to optimize within.

This all relies on you being able to set good requirements from the outset, which can be done by understanding what you're setting out to achieve (the problem you're trying to solve).

I have a comment in this thread which discusses the consequences of this rule specifically. https://news.ycombinator.com/item?id=37069168