neck strength is a big one. getting 'rocked' is when your head bounces around on the inside of your skull - so the more your head moves when it gets punched, the more likely you wont be able to 'take' aforementioned punch.
There are certain neck strength exercises you can do to raise your ability to take a punch. It doesnt mean you'll turn into mark hunt overnight, but they are certainly meant to help. Google is your friend
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