As for how to get one of those magical mind-melding moments to take place in a performance, Jerry Garcia has said, “You can’t make it happen by acts of will.

“There are times when I spend the whole night thinking about things like, ‘God, my feet hurt,’ or ‘I gotta pay the rent,’ or “Why can’t I get my guitar in tune:  it doesn’t sound quite right.’  I never get past the trivial little bullshit so I never see the audience, I never see anybody in the band.  

“But sometimes on those nights people will come up to me and say, ‘God, that was the most incredible music you guys have ever played.’  And I just go, ‘What?’  I listen to a tape and it sounds amazing.  And I say, ‘I don’t remember that.  I didn’t play that.’  And it’s in those moments that I realize that my conscious will, the me I know of as the day-to-day me, is just not very involved in this whole thing in a way that can interfere with it...or cause it.  

“I trust it because I know it’s not me.”  

. . . .

Source:  The Grateful Dead Reader, edited by David G. Dodd.