In theory, etiquette is a way for everyone to express mutual respect for one another. In practice, it's a confusing set of arbitrary guidelines not everyone follows.
For instance, the next time you're eating at a restaurant or even at home, notice how many people put their elbows on the table. For some diners, an all-arms-on-deck approach to eating is an unforgivable transgression. To others, you'd look stuffy if you didn't lean in to engage in conversation because you were more concerned with your posture.
Once you leave the comfort of your home, whether or not other people will conform to your expectations on various types of etiquette is out of your control. You might think "sir" and "ma'am" are passé ways to address people, while others might think you're rude if you don't. And who knows if anyone still cares about where your elbows are when you eat?