I suppose if you've never bitten your nails, there isn't any way to explain the habit. It's not enjoyable, really, but there is a certain satisfaction - pride in a job well done.
I got bitten by the free software bug in February of 1998 around the time of the Mozilla announcement.
Companies are getting bitten by hiring a data scientist who isn't really a data scientist.
If you don't have a tonne of optimism, you're not going to make it... you won't be able to evangelise to everyone else. On the other hand, if you aren't constantly paranoid about what can go wrong and put plans in place, then you're going to get bitten at some point.
I've fallen down crevasses, been bitten by snakes, been knocked unconscious, had various limbs broken and once, a heavy camera came plunging down which very nearly decapitated me.
I did the one concert, and I was not bitten by the conducting bug, and I thought I was done, but then the phone started to ring, and gradually, over time, I started conducting more and more. Now a third of my performances are with orchestras.
I believe I deserve everything that could maybe happen. And I don't think that's a cocky thing to say because I've worked really hard, and I've never bitten the hand that fed me, and I've always been really respectful.