I think this is an interesting question and here is my take on it:
Suffering does not make people stronger - suffering makes people weaker:
If someone breaks their spine, they are made weaker in a physical sense. Even if they recover to the point that they can move freely again they will still be at a high risk of breaking their spine a second time.
If someone suffers from depression and attempts suicide, but later learns to love their life and be happy, they are still statistically more at risk of attempting suicide a second time than someone who does not have a history of depression.
Therefore, people who have previously broken their spine or attempted suicide are at a higher risk of paralysis and suicide, respectively.
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While I am not saying that someone with depression or a broken spine cannot fully recover from their traumatic experiences, I do not think that such a thing happens very often. I wish it happened all the time, but sadly this is not the case.
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Therefore, I argue that people are stronger - on the whole - if they have not gone through suffering in the first place.
Of course, there are some things that are made stronger in the absense of something else: for instance, look up Og de Souza on youtube. This guy has no legs to skate with, so instead he uses his arms. As a result, his arms are really strong - easily stronger than mine (and by the way, he can skate better than me too). What a legend.
Also, someone with autism may suffer in areas of social communication and interaction but in other areas be incredibly gifted.
In conclusion, while I think that suffering makes people weaker on the whole, there is still something to be said about people who adapt to these poor circumstances. When somebody loses a part of them, they compensate by making another aspect of themselves stronger than it was before the trauma. The reason for this is that they are challenged to use new muscles or to think in ways that they have never thought previously.
So they become weaker in that they lose something, but they become stronger in the sense that they adapt to that loss. I'm not sure if any of this made any sense, but that is my take on the question.