However, I don't just sit around doing nothing, a lot of the time. I attribute this to external motivators. This applies, as far as I can see, to almost every aspect of my life. To give an example: I know how to cook, but if I'm cooking for myself, I'll probably be lazy -- I might just eat something straight out of the packet! -- but if I'm cooking for myself and others, I'll go to the trouble of making something good.
I've recognised this in me for some time; the reason I bring it up now is because it's related to procrastination -- which was a hot topic on HN a couple of days ago -- and because I'm interested in doing a PhD. That requires enormous amounts of internal motivation, for several years straight, when there's little-to-no external motivation. I see that this could therefore be my downfall.
How does one develop and maintain internal motivation? What can one do, for example, to renew their enthusiasm if/when it starts to dwindle? Besides "passion" and "enthusiasm", what are other people's internal motivators?