I guess I was just raised in a very frugal family, and those habits remain through into adulthood.
For example, turning off the lights when you leave a room.
40 years ago there was a power shortage, so it was probably more important to turn off all electrical fixtures you weren’t using. But I am still insistent on it to this very day, nagging my kids about turning off lights. I know it wouldn’t make more than a few cents difference on the utility bill, but it still feels like a big deal to me. The same thing goes with the thermostat, which I watch constantly, and adjust it several times a day for maximum efficiency. Although I mess around with it a lot, I decided I did not want to act like my parents did when it came to the thermostat. As a kid, I thought that touching the thermostat was one of the Seven Deadly Sins, this is how mad my folks got about it! Although I don’t like wasting money, I also don’t want my kids to see me act like that over something as trivial as running the A/C a little bit more. So I have a rule where the kids are allowed to turn on the air conditioning if they get hot, but they have to tell me about it first. This way I can see if the house is genuinely too hot, or if someone just left a window open and is trying to air condition the whole neighborhood. Oh no, I already sound like my parents!