For a long time I was utterly useless at bike maintenance, even repairing punctures seemed like a right old faff. I either put up with non-optimal performance or took my bike into the shop if it was anything more serious.
I only started properly wrenching on my bikes five years ago, when I was given my father-in-law's lovely 1960s Cinelli, and had to rely exclusively on my bike for transport for a little while.
Working on the bikes I relied on to get to work was too stressful at first, so I bought a couple of old junkers to strip down and rebuild, generally do up and learn my way around a bike. I put up a build thread on here, asked loads of questions, and learnt a lot. I still have and love the 1950s Raleigh Sport, which is now the first of many bikes I've restored.
https://www.cyclechat.net/threads/1940s-raleigh-rescue-should-i-or-shouldnt-i.168167/
After that I discovered mountain biking and went through a similar process on a late 90s MTB - again I learnt a lot as bike tech obviously changed quite a lot from the 1940s to 1997.
Those builds were all pretty painfully slow and riddled with mistakes that I subsequently had to fix, but by the end of it I'd got to grips with basis on which all the various parts of a bike function, picked up a degree of mechanical sympathy, and learnt what bodges were appropriate where necessary. This was enough for me to do all my own work on my (and a lot of my friends!) bikes.
Since I've never owned a carbon bike I'd still be very wary of working on this, as I don't have a feel for what torques are appropriate where. Never worked on hollowtech BBs or cartridge bearing hubs yet either, but I'm sure I could puzzle these out if I needed to.
I didn't realise how addictive rebuilding bikes can be though... since then I've done up two or three each year, from BMXs to full sus MTBs to vintage racers. I'm even gradually managing to turn a small profit rather than a small loss in the process!
For me, wrenching on bikes is now a second complementary hobby to riding them.
I've not yet built a wheel from scratch (though I've trued up some thoroughly knackered ones that had been in crashes). I'd like to have a go at a fancy snowflake lacing pattern one day.