Okay, here's one you can apply to your real, daily lives (well, some of you, anyway). When does throwing a stronger punch/kick (something along those lines) require using less strength/energy than throwing a weaker one?
No, there's no esoteric Zen metaphysics at work, here. Nothing but classical European physics.
Edit: Also, English is a bit ambiguous for the question. I'm asking when is it necessary to punch weaker in order to punch stronger?