The broadest definition of addiction I've heard is "When you do something compulsively enough that it's affecting the rest of your life" - the implication being that everyone compulsively do things and that's fine but it's only really a problem when it damages your relationships, careers, happiness, etc. All brain stuff has a chemical component but chemical dependency/addiction is a particuarly dangerous subset of ad…
"When you do something compulsively enough that it's affecting the rest of your life" Similar to what I was told: "When you compulsively do something despite it having negative impacts on your life"
But I like framing it this way because if you only think about compulsion you're going to waste a lot of time shutting down things that don't actually matter. We're creatures of habit - we've gotten this far BECAUSE of compulsion, not in spite of it.