Oh, let us take a couple of pure hypothetical example, two first are from multi-playing.
Example 1. Player A DOW Player B's vassal. Player B joins in to defend his vassal. After a few years player B has had enough, and make peace with player A. Player A then kick the vassal big time. According to the posts in this thread Player A is _so_ stupid because he refuses to make peace because he is winning.
Example 2. Player A DOW player B. Player A does not bother to first take his vassals troops, but DOW and takes three provinces from Player A in a quick peace. After the peace player A realise his vassals have also DOWed Player B, but since player A is now out of the war, player B is kicking the vassals butt big time. According to the posts in this thread Player B is _so_ stupid because he is taking vengeance on the vassals.
Example 3. Moslem Kingdom A declare war on Player B. Soon there after also the vassals of Kingdom A DOW Player B. Player B offers all his treasury to Kingdom A, who accepts. Player B then proceeds to annex the vassals of Kingdom A. According to the posts in this thread, Player B is _so_ stupid because he refuses to make peace with the vassals and intends instead to annex them.