Hmm... I guess it must have been Sun Tzu, the author of The Art of War. His main principle: In order to win, complement Yang with Yin, and vice versa.
It has been said that it's best to fight a kicker in a phone booth. How is your typical Tae Kwon Do practitioner going to cope? The only problem with that, of course, is that there are hardly any phone booths left nowadays...
By the same token, I once watched a full contact match between a Kyokushinkai and a Wing Chun fighter. The WC man's aggressive flurry of punches put the former under a lot of pressure, so he stepped away and fired one devastating front kick to the mid section which sent Mr. Kung Fu to the mat immediately.
These examples illustrate that it's good to have different kinds of tools in your tool box, so you can adapt better to the job at hand (or foot).