Asking what your opponent wants to do is a simple question, but we don't always ask ourselves that question. Then, "What does White want to do?" (White's last move was Na3)
White wants to play Nb5 and Nd6+ (or at least Nd6). So Black must play a6 to prevent.
Asking what your opponent wants to do is a simple question, but we don't always ask ourselves that question. Then, "What does White want to do?" (White's last move was Na3)