alt Hacker NewsI have never looked at a fan that isn't running and been confused by the switch being set to “on”. The affordance is that it immediately tells me that the switch is on, so the problem is somewhere else. Compared to the typical phone's “hold for 3 seconds to turn on, hold for 10 seconds to enter some debug mode”, this is a breath of fresh air when anything unusual is going on with the device.
I live in a country where the socket on the wall the fan is plugged into also has a switch, which could be on or off. So to make the fan go around, both switches must be on; the user needs to know about and have a mental model of serial circuits.
If it’s just a button the user just has to know two things: turn the switch on at the wall socket when plugging in, which becomes habit since childhoood; and press and hold the button on the fan to make it go, which I suspect most children in 2025 can manage. These two things don’t interact and can be known and learned separately.
As you said, the knob’s position tells you about the switch. But it’s the fan the user is interested in, not the switch.
(BTW, if the fan has a motion sensor you can’t tell it’s off by the fact the blades aren’t turning. There’s probably a telltale LED.)