claiming to know stuff when one clearly doesn't

why do some people not want to admit that they may not know everything and that that is not the end of the world???

why are some people not open to the fact that they may not know everything??? 

why do some people want to argue on things that are so clear cut???

fancy claiming that you "grew up in Australia" and still claim that glasses and trousers are singular nouns and thus sentences should sound like this ...."My glasses was broken" (instead of "My glasses were broken" and "That trousers" (instead of "Those glasses").

So much for "growing up in Australia", huh?