I went to to see a talk by Benedict Allen (author, explorer, TV presenter-filmmaker and public speaker) at Darlington Arts Centre last night. A fantastic talk and well worth going to see if he's appearing somewhere near you.
He talk was based around his unsuccessful attempt to make a solo dog-sled crossing of the Bering Straits, which I'd seen on TV the other year, but uses this expedition, and other near-death experiences he's had) to consider what we humans need to keep them going, whether in extreme situations or in our everyday life.
Belief and a purpose where what Benedict considered were needed. The purpose being underpinned by the belief. The belief could be in anything (your parents, a god or whatever), but without it humans just give up.