Here are the folks I know about, and the reasons:

First, my business partner and his wife: They got through solo together. She found she didn't like flying alone, and then family and business demands became a higher priority.

My Uncle: Learned to fly and bought a 172 to fly back and forth between alternate residences, one on the soggy side, one east of the Cascades. On one east bound trip he ran into some weather in the mountains and scared himself. On landing on the east side, he never flew the plane again.

My attorney: Was on his long cross-country during his training about the time Mt. St. Helens was doing its thing. He found himself in a light ash cloud. Visibility was not a big problem, but he got worrying about what the ash was doing to the engine. Once he got back to his base, he never flew again.

A client: This guy operated a string of stove and spa stores. Some on the soggy side, some east of the Cascades. He used his airplane to make tours of his stores. On one particular occassion, he was on his way back from the east side. Once over the mountains he found himself low on fuel and above a solid deck of clouds filling the Puget Sound basin. He did manage to find a hole in the Chehalis area, and between the hole and some scary scud-running he managed to get down at Chehalis. A few days later he ferried his airplane to his base and never flew again.

There are also training stories. I didn't keep a count, but I know that quite a few students started training with my instructor and never completed their training, either with him or with anyone else. There were a variety of reasons, many having to do with the expense, the time, or the difficulty. I observed that those who thought learning to fly "would be kinda fun" had a tendency to quit early. One other aspect is that my instructor takes flying very seriously. If he didn't think someone was serious, he had no qualms telling them he did not want to be their instructor.

I do not want to make any judgements about any of these people. I have scared myself twice in the air and I must admit that it was very difficult for me to climb back into the airplane once safely on the ground. But I suffer from withdrawal if even a few days pass without flying (and sometimes my schedule and the weather conspire to keep me out of the cockpit for weeks). It isn't about courage. I am not even what I consider a particularly good pilot (though I am very safety conscious). I just HAVE to fly.

The "fire in the belly" story: A friend of mine offers his services making first-flights in kit-built aircraft. On one occassion just over two years ago he was first-flighting an "Express" (I've seen them, I am not sure who provides the kits). The builder had not properly attached one flap-actuating rod and it was not evident on pre-flight. On his first landing attempt only one flap deployed and he lost control of the aircraft. He was hauled from the wreckage very seriously injured and he was not expected to survive. But he did. His main concern during recovery was his ability to pass a medical and get back in the air. I know that just about any time I show up at the airport, he will be there, and he flies absolutely every chance he can get.

THAT is "fire in the belly".

Reg