Trust and timing and learning to read each other.

That's it, right there--what's so wonderful about playing with musicians you've played with for a long time. The trust and timing and unspoken communication is there. And that becomes critical under performance pressure.

(This is one of those little synchronicities, since the subject of longtime musical companions came up in conversation this evening at the sixtieth-birthday party of a friend from the Irish-music contingent.)