Why does learning by brainstorming and then using criticism work? In answering this I'm going to go on a bit of a tangent.

There is an old question: "Where do things that seem designed for a purpose come from?" For example, a watch is good at telling the time, and it didn't just come into existence randomly. The answer is that a watch had a human designer. But that answer gives us two new questions. First, how do people design things? What's the underlying process? And second, humans seemed designed, where did they come from? If you say humans were designed by God, then we can ask where did God come from? Attributing everything to a designer can't tell us where the first designer came from.

This question is equivalent to, "How is knowledge created?" Things that appear to have a purpose are things with effective knowledge that is able to accomplish some purpose. When I solve a problem, I'm looking for a solution that's going to accomplish my purpose.

Another way to phrase it would be that this thing, which we could call purposefulness, or knowledge, is adapted to do something well. Knowledge is also the same thing as adaptation.

The question of designers, and purpose, and how humans could exist (and cows too, since we know that people didn't design cows) has been answered. The answer is evolution. Animals and people evolved. Evolution explains how complicated, purposeful things can come from only simple, unpurposeful ingredients. So there's no problem of the original designer.

It gets less attention, but evolution also answers the question of how people can design things. It's the same issue of design, and the same process that goes from simple things to more interesting things is at work. Or in other words, evolution is behind intelligent human thought.

How do you use evolution to create good ideas? By brainstorming a bunch of ideas, including new versions of existing ideas, and then using criticism to kill off flawed ideas. This is the same process as evolution. It's not a metaphor but literally, exactly the same thing. So that's why it works.

You may wonder how you were able to think intelligently without already knowing this. Doesn't that mean you were doing something else before? Actually, unconsciously this is how your mind works, whether you know it or not. But if you know it consciously, you can think even better.