Seriously, if I read one more one star review on amazon regarding a person who broke a key off in their lock, I'm going to lose it. Read the instructions. It will tell you that a lock should never, ever be forced. I have two locks with tight tolerances. They have to be fully seated before you turn the key, but when they are fully seated, they turn like butter. One of them even spent a whole year outside rain or shine and works beautifully, still.

If you feel any resistance in a lock, release the death grip on the key and reseat the shackle before attempting to turn it again. This will keep you from having to hack through a tough lock because you hamfisted a key in half.