How OOP Developers Think

Classes in object-oriented programming are all about grouping data and behavior together in one place: an object. Object-oriented programmers tend to think about programming as a modeling problem. They think:

"How can I write a Human class that holds the data and simulates the behavior of a real human?"

To provide some contrast, when functional programmers aren't busy writing white papers, they tend to think of their code as inputs and outputs, and how those inputs and outputs transition the world from one state to the next:

"My game has 7 humans in it. When one takes a step, what's the next state of the game?"

Both Paradigms Are Useful

OOP isn't the only pattern for organizing code, but it's one of the more popular ones. If you understand multiple ways of thinking about code, you'll be a much better developer overall.