Hmm... This explanation doesn't work for me. Tactics is more of a form of warfare than diplomacy, isn't it? In the case of roots like "robot", "electron", or "magnet", the addition of "ics" relates directly to the meaning of the root, whereas the meaning of tactics is significantly different than that of the root, so as a suffix-type clue, I think one of the roots I mention would work, but I really don't think "tact" does. Other thoughts or debate?