"Hmmmm, Mountain Dew.... Hmmmmm,..."
Actually, I find myself reflecting a lot on what future maintainers of my code will think of what I'm writing. Every programmer has inherited code that's a nightmare to look at, and sometimes we get lucky and find an example of forward thinking design, where the author obviously thought hard about making the software flexible and clean in the knowledge that somebody else down the line would most likely have to augment or modify it.
I want to be the guy that future developers see as having made their jobs easier by coding thoughtfully. Conversely I don't want to be the guy that they think about and shake their heads, like the original (and long gone) programmer at my last job whom we roundly mocked for doing things like declaring every single damn member function virtual in some deeply misguided attempt to write flexible code.
I don't know that this translates into mantra per se, but it is a recurring thought that guides much of my work.