A chance remark about brakes left unhooked reminded me of the all-too-frequent scene in a busy bike shop, in which a mechanic gets interrupted in the middle of a long job. In a shop with a small staff or an unevenly trained one, this can happen a lot.
The technician has to backtrack if the interruption was a long one, to make sure nothing gets overlooked. It's not quite like an obsessive compulsive counter having to start over again at "one," but it slows things down.
In the first shop I worked in, the workshop was in the cavernous labyrinth of the basement. The mechanics never had to deal with walk-in customers. They developed their own subculture down there. Whatever else might break their work flow, customers did not.
We still ended up working into the night because none of us had anywhere else to go. Even without direct distractions, it was easier to settle into the groove after closing than during the posted business hours. Upstairs staff could slide into a work station to bang out a few repairs or assemblies.
The guy who fixes my car has slid into a semi-nocturnal schedule to get his work done. He occasionally has someone to answer the telephone for him, but most of the time he has to take care of everything. He became a creature of the night to gather a reliable few hours of uninterrupted work time.
We don't have the luxury of concealment where I work now. I can gain a little elbow room just by being surly, but that only goes so far. So that means trying to put the time in early or late when customers bring us a pile of work.