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.
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.