Programmers often discover solutions while explaining a problem to someone else, even to people with no programming knowledge. Describing the code, and comparing to what it actually does, exposes inconsistencies. Explaining a subject also forces the programmer to look at it from new perspectives and can provide a deeper understanding.
Real thing by the way. Works not only with programming.
came to say this and in addition its more effective with an actual person even if they don’t say anything. Even a small amount of feedback helps that much more although ironically though it kinda palteus if it stops you from jumping on your new ideas and getting them down.