In terms of motivation for a specific task? I have no motivation at all for tasks that I can't place into a wider system. I'm like a kid that never grew out of constantly asking, "But, why?".
In more general terms. I try (not always successfully!) to take Kraftiekortie's attitude - to aim for greater happiness and satisfaction in my life, and to do what little I can to encourage and facilitate the same for the people around me.
Or maybe, as I was once told, my purpose is simply to serve as an example to others of "how not to do it"!

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When you are fighting an invisible monster, first throw a bucket of paint over it.