OOP Isn't a Fundamental Particle of Computing
>  I use lists and strings and arrays with no concern about how many elements they contain or where the memory comes from.<p>You should worry. If you don't want your server or your app to run slow, you should worry about these things. Can you imagine going into a programming interview and saying something like this?<p>It's pretty difficult to implement reliable, readable and proven design patterns if you're just passing around dictionaries of dictionaries and lists. It's more difficult to test. I'm not saying everything needs to be a class, they're a nice tool to have in your toolbox. Use when needed.