Its yes or no...not maybe.

The decision to draw your weapon, not shoot, but even draw your weapon is a yes or no decision.

My CCW class instructor said simply put "If you have to ask, the answer is no".
And I like that. If there's a doubt in my mind, if I have to pause and think about it, then obviously I have some time, therefore the threat isn't imminent and subsequently I can beat feet out of there.