Consider the metaphysical question of whether God exists (just as an example). There are, and have been throughout history, billions of atheists, billions of Christians, and billions of people with many other beliefs. Consider the top million most educated/intelligent/logical among each group. A million people, in spite of their knowledge, intelligence, and education, are wrong on the issue of whether or not God exists (i.e. either the million atheists are wrong, and God exists, or the million Christians are wrong, and he doesn't). Admittedly, maybe we should only take the top from the past few decades, who would have heard all of the arguments made by the others over the millennia, but the idea still holds.
What about the person of average education/intelligence who wants to know the truth? What makes this one person's opinion any better than the million on either side? Shouldn't he just abstain from even considering one option to be more likely? He, who is of average intelligence, and hasn't heard all the arguments, and has thought about this question only occasionally, presumably misunderstands the arguments or positions of the greater minds that came before him.
And even if he thinks he's heard all the arguments, and is perfectly well thought out, his confidence in a position doesn't, in any way, increase the likelihood of this position actually being correct. What's much more likely is that the person fell into whatever trap that the million wrong people fell into, and that even though he is very confident in his opinion, he has been "pushed" by his biases or other limitations. He has no more reason to be confident in his opinion than the million people that are confident in their opinion, but are in fact incorrect.
I am unsure why I should be confident in any opinion I formulate, because I feel I am no more intelligent and unbiased than the millions of people who felt the same way, and were still wrong.