Another element of this question, is stating opinion or supposition as fact. For far too many people, if they think it, it must be true.
If asked a question, or I think I have valid input, I'll speak up. But I do try to prefix my response with a reasonable assessment of my certainty. I'll use phrases like, "I think" (some self-assembly was involved), "I'm pretty sure" (a fair bit of self-assembly and/or double-checking was involved), "I believe" (aka "I heard from a reasonably reliable source"), and the likes.
I think "I don't know the answer" is often a cop-out, what they really mean is "I can't be bothered / I don't care". But if it really is the answer, then you should own it, something like, "That's not really something I've needed to deal with" is a good less "I don't care" type alternative. Personally, I go for my best guess, prefacing it with something like, "Possibly", or or "I think perhaps maybe" (ie. sprinkle on uncertainties to taste).
What I also hate, is the "you just don't like to be wrong". Well, duh… does ANYONE? I mean, sure, some people just like the sound of their own voice, so any answer is a good answer, to them, but still… A better question is why don't you like being wrong. Is it ego, or simply because you'd rather be right. Unfortunately, it seems to be ego for most people. In the latter case, however, and this is something I've found a lot of people have a hard time understanding — except those more scientifically inclined — is that if I am proven wrong, that only means I've learnt something new, and that's quite often even more exciting than actually having the right answer (which is just a nice minor affirmation). So again, eschewing "Sorry, I don't know the answer" in favour of showing interest and offering up what I can, gives me a foot in the door for learning something new, and I always (well, almost always) prefer that over holding my piece and remaining ignorant. It does seem a distressing minority who hate been wrong (and you should hate being wrong) less than they hate being a fool (not to be confused with being made out to be a fool, but that goes back to ego, and properly stating certainties).
This forum is an example… If I offer up some advice, like this very post here, it'll automatically subscribe me for further responses. I put forth my opinion, and now I've got my food in the door for future learnings. Sure, I can hang around regardless — just click the Notify button — but doesn't that seem a little more, stalkerish? It's like hanging around near a bunch of people having a conversation, evesdropping…