I am one of those people that when in a car never passes. Yeah, it's fear. Yeah, I don't want to screw up and get into a head-on collision. But it's also because even though I have been driving since I was 17 (yeah, late bloomer) I have yet to figure out how to make a car speed up really, really fast. Since I don't have a clue how to do that, I know I'm going to be very slow in passing and need a LOT more clear space than most people.
(And I know it's me and not the cars. My husband and I will test-drive one, I'll be in the driver's seat and I decide to see how fast I can accelerate. And it goes up so slowly despite me having the gas down. I'll say "Hon, I don't think this car has get up and go." He'll get in the driver's seat, get going and BAM! We are going from nothing to really fast quite suddenly.)
However, because it's an issue at my end, I'll stay back until I'm sure I can pass safely. Sorry for the folks behind me, but I'm #1 in my mind.