Most of what you learn in CS is a bunch of words you have no idea what they mean until someone gives you a precise definition. Deterministic Finite Automata, regular expression, static typing, serialization, compilation, singleton pattern, etc. are all terms we use every day in our profession, but it's not clear what they mean. But we read the definition, forget it, someone reminds us, we forget it again, we implement it and we remember. Same with monoids, functors or monads, we need to take some time to learn what they mean and then we can include them in our vocabulary.