Its maybe worth remembering that although we should all be capable of some servicing ourselves (and can get enormous pleasure from doing so)...not all of us have the equipment, time or skills.
I'm an engineer, have no problem taking on most tasks...but....
3 bikes over 6 years, many thousands of miles covered...i have never had to touch the gears.
Ive done everything else, stripped headsets, replaced stems, cassettes, stripped freewheels, overhauled wheel hubs, strip and cleaned brakes, derailleurs, BBs....but never adjusted gears.
Would i want to...yes. Will i if i need to...no.
There's even videos on Youtube i think...but you still really need a stand before you even start. Can i be bothered...no.
5 minutes in a bike shop....job done.