Learned by necessity, because I was poor and made whatever bikes we had work with what tools were available or cobbled together.
Made mistakes, bled a little.
Changed tires with rusty screwdrivers, poked holes in the tube, learned to patch tubes.
Learned better techniques, stopped piercing tubes when changing tires, kept patch skill for punctures.
Same goes for chains, brakes, bearings, mix and match parts, fit, derailleurs, and tire lacing.
Later came the skill of judging if the investment in time exceeded the savings in $
(still working on that one)