Often, I think I understand something very well. (maybe "think" should be replaced by "feel")
When I start to explain it by a writing artifact, then I feel I hit a wall.
Maybe Einstein is right
"You are not really understand it, when you can't explain it in simple manner".
Thinking is reduction of feeling
Speaking is reduction of thinking
Writing is reduction of speaking
so.... once I can write about something clearly and simply.. than..I can be proud that I really understand it.