How many times have you heard a player say, "but they can't be THAT smart! They're just dumb monsters!" - or words to that effect? Translated, what that really means is, "I can't believe monsters would use every tool at their disposal to survive!"
It is essentially an argument for making life easier for the players. Hey, c'mon, we're the heroes - gimme a biscuit. I don't like this argument for at least two reasons. One reason is that it stems from the information given in The Monster Manual for AD&D 1st Edition - every monster got an intelligence rating, and players memorized that information to use to argue with the referee. As has been noted elsewhere this is the sort of thing that leads eventually to every monster having a stat block and the game turning into an exceedingly complicated simulation (but potentially not a very fun game, or so it seems to me).
But there is also a deeper philosophical argument here I want to make: the player characters are NOT heroes. Far from it, insofar as D&D is concerned. If anything, player characters have the chance to become heroes, by displaying heroic behavior. And heroic behavior should not be easy. Monsters ought to be implacable foes, ready, willing, and able to do their worst to survive. Otherwise you might as well let the players do whatever they want.
After reading some of the background on Tucker's Kobolds, I immediately thought of players making the argument that monsters simply would not be smart enough to be a "real" challenge. Such an argument actually cheapens any accomplishment by the players over their foes, so I found myself beginning to think more about how to make monster encounters tougher - if that's the direction required. After all, player characters need to be able to tell the difference between knowing when to fight, and when to fight another day, if they really want to be heroes.
November Campaign Design IX - Campaign Map
56 minutes ago