If you fight with someone who is good at boxing, you can find it challenging. You see that the straight punch, uppercut, hook, and jab keep coming. You are defending some punches, but he continues punching. So how long are you going to defend that?
To defend against punches, you step backward. Will it work? Well, you can step back and make some distance between you and your opponent. A boxer is good at footwork. He will immediately close the gap. And you will see the punch land on your face.