Human: Why is the sharp variation 9... Re8 10. 0-0 c4 unattractive from Black's point of view? Assistant: 
The sharp variation 9... Re8 10. 0-0 c4 is unattractive from Black's point of view because it requires Black to know a lot of theory just to secure a draw. The sharp variation 9... Re8 10. 0-0 c4 is objectively the best move, but it is not clear that Black has equality.