Final answer:
Barrett learned the importance of being cautious and aware of the potential dangers when he took the gun from Snyder.
Step-by-step explanation:
Barrett learned that taking the gun from Snyder had put him in a dangerous situation where he had to constantly be aware of the gun and its potential use against him.
He realized that relying on the sound of the gun's shot was not enough to protect himself, as the gunshot arrived too late after the bullet had been fired.
This experience made him understand the importance of self-defense and the need to be cautious in similar situations.