R – Which Computer Science Concept Do you Value the Most

For some reason, I notice that I end up using a lot of finite state machines at work. In particular, when I'm implementing a custom TCP/serial protocol, they are very helpful and produce a very robust output (in my opinion).

My days in CS classes are long behind me. As such my recollection of the stuff I learned there is fuzzy. I was curious if there are other concepts people are leveraging that I've forgotten about.

There is no "right" answer. Vote up the answers containing the concept you use this most. We'll simply end up with the most used concepts on top. For me, it'll be a list of stuff to study up on.

-Robert