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Pantah describes well what I think too. Probably most people can do a great majority of work on their bikes, with minimal instruction. Youtube videos are great. Adjusting derailleurs, brakes, and bearings are all pretty simple (and I distinguish that I'm only talking about mechanical, cable-operated devices here. I leave electronics and hydraulics to others). I think wrapping bars and building wheels requires greater knowledge, which comes from more experience. It also comes down to knowing how to use some of the more specialized tools.
Reading here over the years about the difficulties some people have with various repair procedures, from installing tires to centering brakes to everything in-between tells me lots of folks here would be better off taking their bikes into the LBS. The extraordinary lengths of many rear brake cable loops (and some front brakes) convinces me. But they persist in doing things beyond their abilities, which is fine, and their prerogative, but will always result in my SMH.