Why do some people have a higher pain tolerance than others?

I sometimes feel like my religious experience isn't real because I live in a middle class neighbourhood and don't have serious probems like famine, starvation, war, disease, crises at home, or humanitarian missions etc... I admire people who raise funds for charity by climbing mount everest or become soldiers in the army and want to help their country - I don't think I would have the courage to die for my beliefs or perform physical acts of extreme difficulty and my lack of strength seems to dim down my religious faith. Why do some people have more tolerance than others?
Why do some people have a higher pain tolerance than others?
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