This is a question I have asked myself many times when watching or reading sci-fi stories.
Very rarely do you see that the technically superior, infinitely advanced and stupendously intelligent alien conquerer wannabes actually win the fight. In the end they always have some weakness that causes their downfall.
In Footfall, the attackers have absolutely no idea about deceit and general dishonesty (although we, as a species, have raised it to a fine art). In Harry Turtledove's World War series, the invaders are just too inflexible so we run circles around them and steal their equipment. In Star Trek it is our solidarity and good nature that saves us from evil. In Babylon 5, we are the next coming - it being the dawn of the 3rd age of mankind an' all!
The oversights displayed by the seemingly clever alien species are incredible. The aliens in War of the Worlds only had to expose themselves to the world for them to be killed by a local virus! Again in Turtledove's books, the aliens never realised that in 1200 years,we would be able to go from sword swingings idiots to gun toting maniacs. A simple mistake really.
Whenever we get our hands on a new piece of kit, we somehow use it better than the invaders and beat the shit out of them! The only species that come close to our level of competancy are all less than 50 years ahead of us technologically. Case in point, V! Apart from their flying technology, nothing they had was particularly beyond our grasp.
Humans are the masters of beating the opposition at their own game, even when we should be incapable of playing (Dark City). We can out fly them, and slip in to their most heavily defended areas completely unharmed as in Independence Day, not forgetting that we have the ability to read leaked memories from mind controlling monsters!
Just for once, can't we have a foe that stands a chance of beating us. All these people being abducted is very melodramatic but when are we actually going to be in any danger?
Coming soon: Conquering Alien Worlds in 21 Days