I am terrified of heights, yet I have been skydiving, done aerobatics in an open cockpit biplane, hung outside a helicopter with my camera countless times, have walked across the catwalks in the ceiling of the VAB at Kennedy Space Center, all with no issues. But get me up in a scissor lift or a boom lift at work, and I instantly freeze up.
Now I am much the same way. I can't go around to the front of my roof with its "horrific" 16' drop to the driveway (and it's not a steep roof, 4 on 12). But flying is great, I've been more than halfway round the world in my travels for work. But put me on a high mountain road and you will have a panic-stricken mass of blubbery man in the fetal position on your hands. I hate to walk across bridges and avoid that at all costs, eyes locked straight ahead and moving fast.
BUT.... throw a rope over that bridge and tie a sling seat on me and I become fearless. I was the first in my training group to rappel face first, running down the cliff, because the first two guys who tried froze up. My buddy and I had a bet on a 75' free-face rappel tower, as there was an angle support about halfway down, who would get under it on the first bound, as the tendency is to brake right away and many were almost hitting their heads on the platform - which he almost did as well - and I easily cleared the brace, dropping to the ground as I swung back out from underneath it. When I hit the ground, a stocky Green Beret stalked over to me and said "Don't you EVER do that again!"
And I'm genuinely perplexed, "Do what, Sarge?"
"Didn't you see that bar, you could have took your head off!"
"Oh, Sarge, I watched it the whole time! Ron and I had a bet as to who would get under it on the first bound."
He looked at me incredulous, then whipped his hands down in disgust. 50 years later I can still see his face. A tough old Green Beret named (you can't make this up) Sgt. Hawk.
We then went over to a 100' cliff where I was sitting with some real soldiers from the 101st Airborne. One of the other Green Berets was standing on a tree root with nothing beneath it but 100' of air. And I'm visibly nervous, and the fellow next to me says, "Why don't you go over to that shorter cliff?" I told him I'd be fine once I got on the rope (and I was), but just sitting there with that character standing on that tree root was really messing me up. He replied, "I know what you mean. I'd rather jump out of an airplane than go over that cliff."
So I hope you enjoyed these stories. My point in belaboring them was to show that phobias are not rational. Maybe someday I'll try a tandem jump... But though I like to rappel (abseil), you'll never catch me climbing back up!