Punching and kicking are akin to slapping an attacker around. If you're in danger, you need to throw all your weight into a single target, or "strike." Imagine you're facing a giant predator and you have a big sack full of rocks. Throw a single rock and "ouch!" is the only reaction you're likely to get. But swing the entire sack at him, hitting him in the head, and he'll be out cold. That's the difference between punching and striking.