I've never had imposter syndrome either. I don't really relate to your fractal example. My experience was when I was 13, my older cousin was bragging that he'd used up all the memory on his trs-80 making an adventure game (BASIC). I was very impressed until I saw his program. It was all if/else statements, he hadn't used any subroutines. I was astounded. That was an early lesson to me, no one knows all this stuff. That and the realization that these damn machines make fools of us all at one time or another :)

Everyone is just at different stages of learning. When you've been doing this long enough, you've forgotten a lot you knew before. At some level, 'refreshing your memory' about what your forgot is not much different than learning it the first time.