Math

I just now realized how simple math really is at its lowest level.  If you are familiar with sets and functions, and have a decent grasp on logic, then you understand almost all of math(nice job!).  Of course the most fundamental assumptions have been built upon for thousands of years and, as a result, some of the latest constructions are quite complex.  Creating a model and applying the results to real problems is not always easy either.  Still, math can be boiled down to an amazingly simple foundation, and its truly a marvel that it can tell us anything useful about what's going on in this universe.