Opening the book…
Dependence without understanding turns you into a passenger in your own life, and it quietly makes you afraid of the things you rely on. Repair teaches you how something actually works in a way that using it never will. It also means that when it breaks at the worst moment, you are not helpless.
Pick one: the bike, the sink trap, the code you inherited, the espresso machine, the recipe you always buy. Open it, learn its parts by name, fix it once with guidance and once alone. Keep the tools where you can reach them.
Don't teach yourself on live electrical mains, gas lines, or anything where a mistake is irreversible or voids the protection of others. And skip this when the honest answer is that a specialist's hour costs less than the damage you'd do.