When you have the initiative, you must attack!
Steinitz famously said that the player with the advantage must attack or risk losing his advantage. Except for certain static positional advantages, this is undoubtedly true. The following game illustrates this theme. After 8. Bxc3, white has a nice advantage and attack. 9...g6 was a big error, but I only found the mediocre 10. Bc4. 11. f3? was an entirely passive move in a position in which white has the initiative. Black eventually managed to equalize and win on time. I need to learn better how to keep the pressure on my opponent in situations like this.