tl;dr:Set of guiding principles that help Max write CSS, the first three are to remember that everything is a rectangle, the cascade is your friend & as much code as necessary, but as little as possible.
tl;dr:Often, complex solutions are created to solve complex problems. However, this isn't always the case - "sometimes the smarter way to build things is to try and take some pieces away."
Complexity can arise from the inflexibility of best practices or developers wanting to show off how smart they are. In either case customers lose out.