@saw038,
Some interesting discussion here..
I think what keeps us grounded or upends us is certainly not in any small part our upbringing. But yes, also as has been pointed out, our genetics combine with that upbringing making it impossible to know just how someone will respond to similar stimuli.
I think more generally speaking, I agree with what was said earlier as well about survival being sort of innate. You have a head start just from being alive.
Beyond that I think you have to have a purpose, something that you live for that is outside of yourself. I also think you have to feel valued. These are part of being a social being..
These are general things though. I supposed those with purpose and who feel valued could still be depressed. Robin Williams was apparently valued by family and he seemed to have found his purpose. I guess, outside of outside forces, you can't discount the effect of physiological depression as well. Its hard to really know..our perceptions of reasons to live or die will often reflect our own biases.