I went so far as to ask the receptionist at my chiropractor, Lindsay, about the story you told me - whether after a couple of successful jumps one might still come up with 'the fear' and 'reject the door'. Her opinion (her of 100 or more, I think, jumps, she works at a jump school in the summer) was that the scenario would be unusual, but possible, as the exercise was largely mental, and the equation might add up differently on a given day. She also told me, by way of example, that some people - people she actually knows - who really like skydiving are also afraid of heights to the point they couldn't climb a stepladder, so she felt it was quite different than looking over a cliff or off a bridge for a base-jump - which was also interesting for someone thinking about the whole enterprise in the very abstract.