Here's a position from his game as Black against Ossip Bernstein (Moscow, 1914):
Black to move played 24...Rc6-c7
Capablanca's 24...Rc7! looks like a mistake after Bernstein's reply 25.Nb5: the red arrows in the following diagram indicate attacks against pieces and the green arrows indicates defenses of a piece.
After 26.Nb5: Black to move
Now the poor Black pawn on c3 is directly attacked twice, and indirectly attacked once by the rook on c1 supporting the rook on c2. The knight on b5 is also threatening to win the Exchange (that is, win a rook for a knight or a bishop: an advantage worth somewhere between one and two pawns).
Capablanca decided to save the Exchange with 26...Rc5, and White grabbed the c3 pawn with 27.Nxc3 Nxc3 28.Rxc3 Rxc3 29.Rxc3, reaching this position:
Black to play: find Capa's amazing move