I don't recall the exact answer (and it looks like others have already supplied info) but I saw someone explain it in detail once and wrap it up with a quote fr

I don't recall the exact answer (and it looks like others have already supplied info) but I saw someone explain it in detail once and wrap it up with a quote from the Star Trek reboot: "It's like trying to hit a bullet, with a smaller bullet, while wearing a blindfold, riding a horse."