How do certain thoughts give us energy to continue living in extremely harsh conditions?

Question

Say, a man lost in the desert thinks of his wife and kids, and it gives him the strength to continue. why was this strength not tapped into before?

Answer 1

Don't it always seem to go that you don't know what you got till it's gone. They paved paradise and put a parking lot.

Answer 2

We see our strength best when we're under pressure.
Once we learn the difference between "life and death" situations, we learn what is most important to us.