When someone starts programming, the first concepts he's learning are "procedural" concepts, i.e. how to control the program flow (if...else, for, do...while etc). Another concept is "object orientation". Now you have to think of "encapsulation of data" (how to access them, and more important how to change them safely), and eventually of components and their interactions. Bill mentioned SOLID: those are 5 ways for creating components and having them interact. "S" stands for "single responsibility" and is a good point to start with: a class takes care of one thing only, a function in that class of one action only. This change in paradigm from mere procedural code to object oriented code is a big step. Oh sanctissimi Wilhelmus, Theodorus, et Fredericus!