Consider the ninja.
As we all know, one ninja is a deadly killing machine, an adversary fit to match wits with any hero, who will be lucky to escape with his life.
But a thousand ninjas? Mere cannon fodder.
That's the Law of Conservation of Ninjutsu at work. Ninjas have finite awesomeness, held as community property. The more ninjas there are, the more thinly ninjutsu is spread among them. The Law applies across the universe. One Dalek or Borg is a threat to the earth, capable of defeating small armies. But if a battlefleet of millions should appear, the Doctor or Captain Picard just gin up some technological deus ex machina, and poof! Away they go.
The people behind the TV Tropes Wiki have, to an even greater extent than those behind television without pity, watched far too much tv. And seen too many schlocky movies. And read too many science fiction novels. And played too many videogames. And they've shared the knowledge gleaned from this, in one of the best written and most amusing websites this fellow geek has ever read. A few burning questions answered:
Why are home power tools, so dangerous to you and me, simultaneously the ultimate weapons of film?
Why is it that time travelers can prevent the fated assassination of the President of Futuria one day, but next day the LAWS OF TIME prevent them from killing Hitler, and why is this logically consistent?
How is it that women who possess superhuman strength, like Diana Prince and Buffy the Vampire Slayer, get tied up so often?
Why are futuristic computers, which can understand colloquial speech and calculate trillion digit primes, so damned stupid?
And so on and so forth. TV Tropes is a vast collection of writing, in wiki form, so just clicking on the links will take you to new and amusing pages, where you can read deep thoughts on the archetypes which appear over and over in this stuff you know you shouldn't love, but do.
We write about time wasters every Friday here, but this is the genuine article. TV Tropes can suck up your entire weekend.