"That which does not kill us makes us stronger"
Now, I think most people get the gist of it. I mean, it's kind of self explanatory, right?
Well, I believe it to mean many things. I mean, for one, people who withstand abuse - verbal, physical, mental, and any other kinds of abuse - as long as they come out alive (and sane) they will be able to withstand similar instances in the future. This means that people build up resistance and grow stronger.
But what if you lose a limb? You didn't die, you just lost a limb. How can you be stronger then? In this situation, I think that the quote means that belief also grows. If you don't believe in living because you lost a major part of you, it will kill you. Though, if you do believe, you will live on with more hope. That hope could inspire others and make people stronger as a whole.
Okay. So, most people don't lose limbs. But what if you lost something important to you in any way? A person, a thing, a place, anything, even if that "thing" was a childish stuffed animal. It's sentimental value after all! I think this ties into the belief thing, but I think it also means that the part of you that depends on what you lost wouldn't be so dependent on that thing anymore. Of course that part of your heart would always be scarred, but even some scars heal. Sadness could weaken you, but if you get over that sadness, you would become a stronger person overall.
So remember, in times of sadness and despair, what doesn't kill you makes you stronger, or that which does not kill us makes us stronger.