Relax relax relax!

Yes, the key is to relax.

The more brute force your opponent uses, the more you must relax. That way, no matter how hard he tries, he simply cannot push you. It will be like trying to push into an endless depth of cotton. Whenever his force comes, just relax, turn and deflect the force away. And if he becomes frustrated and uses even more brute force to try to push you, then you have already won. Because eventually, his force will be so strong, that when you deflect it away, his force will carry him with it, causing him to lose his balance.

So when your opponent tries to push you with brute force, be so soft that he doesn't have any place to put his force. Just relax and let his force flow past around you. Eventually, when his force is too great, it will carry him with it. The moment you resist, it becomes a contest of strength, and whoever has the bigger muscles will win.