An example: artificial lighting. Despite most lighting transitioning to fluorescent then LED, total electric demand used for lighting hasn't really gone down as the cost has gone down; people just floodlight everything now. Some napkin math indicates Canadians use about ~10x as much artificial light per capita compared to 50 years ago.
It's not a law, of course, or at least not a simple one. E.g., the cost to refrigerate has come down similarly, but while air conditioning continues to increase in use, average freezer/fridge space plateaued in the 1980s. Everyone seems to now have as much freezer space as they want. Some demands are fully satisfiable and people don't necessarily consume more, even as the cost comes down.
There’s various types of demand - some seem to climb indefinitely (does anyone even bother turning lights off anymore?) and others have practical limits, like fridges and freezers.
Often those limits are the results of other aspects - but there’s not real downside to lighting everything with the fury of ten thousand suns. Besides the dark sky loss.
It's not a law, of course, or at least not a simple one. E.g., the cost to refrigerate has come down similarly, but while air conditioning continues to increase in use, average freezer/fridge space plateaued in the 1980s. Everyone seems to now have as much freezer space as they want. Some demands are fully satisfiable and people don't necessarily consume more, even as the cost comes down.