BIONICLE: The original six Rahkshi from the Mask Of Light saga were depicted as the greatest enemies the Toa Nuva had fought to date, nearly killing them on multiple occasions and only being defeated by the combined efforts of all six Toa Nuva, plus the newly-empowered Takanuva. All later Rahkshi are much weaker varieties, capable of being defeated in droves even by regular Toa (the Toa Nuva are several times more powerful than most of their kind). The Final Battle has them fighting an entire army of them. Justified, in that the original six were specially made by Makuta to be more powerful than average, while the others were mass-produced as quickly as possible.
Theatre example from Police Cops In Space. After the two Police Cops blast their way through the robot army to face their leader, he sneers: "You may have taken out a thousand robots, but now let's see how you cope with...one robot." And in the ensuing fight he kills one of them, and would have won were it not for time-travel shenanigans.
Miyamoto Musashi said in the Book of Five Rings that "one man can beat ten men. Just as one man can beat ten, so a hundred men can beat a thousand, and a thousand men can beat ten thousand. In my strategy, one man is the same as ten thousand".
