If you're not stubborn, you'll give up on experiments too soon. And if you're not flexible, you'll pound your head against the wall and you won't see a different solution to a problem you're trying to solve.

译文：凡是说祸福，是靠自己求来的，就是圣贤之言。若是说祸福，是靠上天决定的，就是庸俗之言。