I get bikes in all the time with the "I do my own maintenance" when what they really mean is "I change the engine oil every once in a while". Not clicking on the clickbait (I am highly skeptical of "top ten" lists on the internet now) but the general point is valid. Steering head bearings, fork oil, wheel bearings, cable lubrication, clutch adjustment, fasteners, etc generally get completely ignored.
Latest example, I just had a bike in that didn't appear to have had the wheel bearings repacked since it was new. Brand new tires though. Apparently he takes it to a "tires only" shop that didn't bother (or didn't know enough) to look at the wheel bearings and suggest that they be cleaned, inspected, and repacked.