On fear of "exposure" or to give it its technical name "acrophobia"...
As a sufferer (and as aircrew) many moons ago it was explained to me thus.
Man desires to fly
Some men desire to fly a lot (strangely they often become aircrew)
Men who desire to fly lots go up building/cliff/mountain
subconscious mind says..."you want fly...jump, it will be good"
Conscious mind (also known as fear) says..."are you out of you ****ing mind, get away from the edge!!
What we aircrew hear and feel is our conscious mind responding to our subconscious desire.
That is why we love being in an aeroplane or dangling from a harness (where we are secure) but hate being at an edge, where we are exposed.
It made sense to me