> it was possible to believe that I had been placed on earth for the sole purpose of providing her with that last ride.

I suspect that a lot of people have a "heroism gene". In situations in which they're doing something selfless, and nothing matters other than helping the person before them who really needs it, there's an implicit "this is my purpose" or "this is what we do".

I've wondered where that comes from, nature or nurture. And how common it is.

And also how that changes once they have family dependent on them, when helping someone else would threaten that.