Fear as a Motivator

Fear is perhaps one of the greatest motivators known to man. It is that way because our survival is bent on fear. Evolutionarily, fear is perhaps one of the most beneficial things to a species' survival - as well as things like physical traits that help a species survival and eliminating competition. But if the competition is too great, then we avoid it, therefore we fear it. If a certain environmental factor would kill us - we stay away from it. We're adapted to be scared of things such as snakes, spiders, etc.
I had once read a quote of how humans were adapted to fear spiders and snakes, but not cars. Just thought that was interesting.
An interesting way to think about it is if we fear something, yep we defy it - does that mean we no longer fear it? A great example of how fear could be use with extreme efficiency would be something like Thomas Hobbes' Leviathan.