While reading this thread a thought occurred to me concerning mechanical "ability".Some people might have intuitive mechanical ability but never know it because they were never encouraged to, and in some cases discouraged from, work on mechanical things. Many of us were encouraged by parents or education to value abstract , intellectual pursuits, and not to work with our hands. So maybe taking apart and rebuilding old bikes is a way to find out if you have ability.

On the other hand, there are idiots who work as mechanics (auto mechanics and offshore oil well technicians), who have very little mechanical ability. The results are disastrous.