I know next to nothing about advertising online, so please don't think I'm being facetious by asking this: what is the actual rate of display ads vs. people that click and buy stuff directly resulting from that ad?

From what I heard it's sub-10% or even 5%. If 5% is considered good, doesn't that say something about advertisements, that is, that 95% of the people _didn't_ follow through, and probably ignored it. This to me screams that there should be a better way to advertise.