the main axis / cross axis thing is what actually stuck with me. I used to just memorize justify-content = horizontal and align-items = vertical, worked fine until I used flex-direction: column and everything flipped but my mental shortcut didn't, so I spent way too long debugging something that wasn't even broken lol

also glad you added the "don't use flexbox for everything" bit at the end. I went through a phase of forcing flexbox onto layouts that were obviously 2D just bc grid felt like one more thing to learn. have you gotten to the point where you know upfront "ok this needs grid" or is it still kind of trial and error for you too