Creatures really have divergent and conflicting desires. Their distinct motives are not (usually) wishes for survival or for means-to-survival, but for various particular things to be done and obtained while surviving. And these can always conflict. Motivation is fundamentally plural. It must be so because, in evolution, all sorts of contingincies and needs arise, calling for all sorts of different responses. An obsessive creature, constantly dominated by one kind of motive, would not survive.

Beast and Man: The Roots of Human Nature (1979). 168.