From Lessons in the Fundamentals of Go, by Toshiro Kageyama:
Problem 6.
Black to play. He has succeeded if he can link all his forces together. At first it is hard to see where to focus, so read the sequence out slowly and surely.
Okay, I was able to read the first part with only a little pondering.
Bzzzzz! Wrong!
This is the correct reading. (9 is in the spot marked 20, captured by 18.)
Kageyama says even a novice player should be able to easily read 20 moves ahead. :-(
Seriously, I have real problems visualizing that many stones that aren't actually on the board and it seems to be an issue with how my brain works, because it's certainly not a lack of intelligence. If I can't train myself to read ahead more than three or four moves, I will always be hopeless at go.