Until you encounter a switch that's part of a three-way switch arrangement where up can be on or off depending on the position of the other switch in the circuit.
I've lived with these my whole life, in every place I've lived, plus with one or two switches that were sideways, so the first time I'd ever heard "up is on" was in a comment thread like this a few months ago. I didn't think there was any sort of standard, it's just always been "flip the switch if it's not currently what you want".
Izkata|2 years ago
This is in the US.
nerdponx|2 years ago