Super Fly Or Useless Spider?

I am sitting at my computer with a fly buzzing around the room. It’s annoying and if it continues and attempt will be made to swat it. My observations of the flying menace have revealed it repeatedly flying and landing on a spiders web (complete with spider). Just when I think it has been trapped and about to meet its doom it takes off and flies about a little more.

Is the spider at fault for making a flawed web? Am I dealing with a Teflon fly?