What does "discretion is the better part of valor" mean?

It is better to be prudent than merely courageous, as in I'm signing up for the easy course first; discretion is the better part of valor. This proverb, a synonym of look before you leap, was first recorded in 1477. Charles Churchill put it in poetic form: “Even in a hero's heart, Discretion is the better part” (The Ghost, 1762). Shakespeare also used a form of it: “The better part of valor is discretion” (1 Henry IV, 5:4).