[k00b]

Also, Dr. Huberman of http://hubermanlab.com/ has been making the round on podcasts talking about the neuroscience of motivation.

tl;dr We are motivated/rewarded (at the neurotransmitter level) when we feel that we're on the right path. What makes you feel like you're on the right path?

This feeling of being on the right path causes dopamine to be released which quells the anxiety/quit sensation (adrenaline/norepinephrine) that's caused by struggle and is what leads to burnout.