Got it. Now it makes more sense to me. Now I know people tend to talk about atomicity when it comes to low-level-ish things. But say I create some sort of a web service with a bunch of business logic. Does it worth to follow this principle in that case? For instance, client sends an API request (let's say "Add user to friends"), is it even possible to apply atomicity for these type of things?
Edit: Thanks everyone for taking time to explain it to me.
Edit: Thanks everyone for taking time to explain it to me.