This KISS principle is not the one declaring you should rock and roll all night and party every day (although that's a good one). KISS is an acronym for "keep it simple, stupid." The KISS principle applies in a wide array of disciplines such as communication and design. This excellent article from Carrie Allan, a spirits columnist at the Washington Post who the Den has featured in other posts such as The Magnificent Seven of Cocktails, is a reminder that the KISS principle also applies to cocktails.
You can get a lot of great cocktails at bars. However, sometimes their ingredients and complexity make it very difficult and insanely expensive to try to recreate them at home. The frustration can lead to the point where tears are falling (do you get the musical reference without Googling it?). Sometimes simple is best. Whether it's a drink with three or fewer ingredients such as the Margarita or Stiletto, or a drink with equal proportions such as the Last Word, it's easy to make great cocktails at home.
And what do you do after that? To use a line from Gene, Ace, and Paul ... lick it up.