Any problem with a bike is annoying, especially if it causes you to hike back instead of ride. I think the real trick is knowing enough to solve most of your own problems. Not every shop is a good shop, and even good shops will take a while to turn around your bike. IMO Skills a new rider should prioritize are:
- flat repairs,
- if you go tubeless know tubeless set-up (even if you want to cheat and use the http://www.fattystrippers.com system).
- broken chain replacement and how to check for wear.
- derailleur adjustment basics, including hanger alignment because that gets knocked so often
- brake adjustments, pad inspection and changing.
- greasing what needs greased, oil on what needs oil and blue loctite on what needs to stay put, and knowing the difference.
More extensive repairs like linkage bearings or shock rebuilds is where I tap out. But I have come to enjoy wrenching on bikes and have saved quite a bit of money doing it.
I’ve ran across people on trail who really had no clue. I was able to help them but they could’ve had a LONG walk back and could have easily remedied their own issue with a little knowledge.