Georgian windows.
Georgian windows on a foggy day.
Leaded windows on any day.
Deep seated windows where you have to detail every edge.
Those weather conditions that cause the edges of the glass to 'bleed' back out leaving you no option but to waste time polishing the edges instead of a quick bit of detailing.
turning your rubber when the first side has worn, only to find a tiny 'nick' on the fresh side and not having your spare rubbers in the car

knocking over bucket full of soapy water in the car and finding the customer is out and doesn't have an outside tap!
Forgetting to tie ladders onto roof rack.
Forgetting the ladders are heavier on the overhang on the bonnet side of the car and then undoing the rear bungee first
Buffing a pane of glass with your scrim and then realising you just spread spider flesh all over the glass, scrim is now rendered useless cos of the spider...you can also replace spider flesh with many other things too, a glob of sticky sweet or a bit of a chip you missed with your scraper

Squeegeeing of a window in windy weather, only for the wind to blow the water back onto the glass
I could go on...but I've got to get to work!
Ian