Wordflow.
Just like runners use music and beats per minute for hitting a stride, I depend on music to help me reach a state of mental flow.
The quality and clarity of my work depends on it.
If you're interested in the neurology behind this, be sure to check out Mihaly Csikszentmihalyi's extensive research.
Andrew Belle is one of the only artists (along with Tycho) that I can consistently count on to help me get centered when my writing depends on rapid turnarounds, sheer focus, and total accuracy.
In other news, I guess I'm kind of a weirdo.