Walking, talking encyclopedias

Why do some people insist they're right when they know so little about what they're talking about. These people also like to force their opinions on other people. The type of people i'm talking about are the know it alls ..... the mr. jeeves from the ask jeeves website or the walking encyclopedias of infite knowledge. Yes, those that are undeniably the experts of anything under the sun (sometimes even experts of the universe). These people literally have or think they have the answers to everything. Ask them something and they'll know the answer to it.
In reality these people are just full of crap. In truth they know nothing. But they make good pyramid scheme sellers, you know the skim cepat kaya stuff. Pyramid selling that's what they're good at, because they're good at b.s. They really know how to talk and you can actually be fooled by some of these know it alls. Not necessarily into buying pyramid schemes but into everyday stuff.
Moral of this posting: Be careful around encyclopedia type people. They can cheat you in finances as well as in love, i'm sure, because they are such good liars.