I rebuilt a bicycle using tools in my dad's garage and basically just guesswork. Then I discovered this website and found out everything I'd done wrong. I had mismatched bearings, crap brakes and gears, you name it.

Must admit, though, this was pre-YouTube. While I do admire written works like this, and I still treasure some of my cookery books, there's nothing like watching someone do these things. Especially things involving subtle skills that nobody would think to write down, like adjusting derailleur gears. Learning by copying is the original and best way for many things.