Therefore the good fighter will be terrible in his onset, and prompt in his decision.
The word "decision" would have reference to the measurement of distance mentioned above, letting the enemy get near before striking. But I cannot help thinking that Sun Tzu meant to use the word in a figurative sense comparable to our own idiom "short and sharp." Cf. Wang Hsi's note, which after describing the falcon's mode of attack, proceeds: "This is just how the 'psychological moment' should be seized in war."