It's even more than that. By qualifying your statements, you let others evaluate them correctly.

So, for instance, if 'tptacek here says a factual statement about security (and there's no large thread contesting it), I'll treat it as gospel. But if he says he's unsure about it, or he read it somewhere, I know to attach less weight to it. I'll code in it my brain as "uncertain, but passed the sniff test of a relevant expert". Etc.

The same principle works in more mundane aspects of life. Whether a person believes something (and how much), or whether they're just reporting something they've read elsewhere, matters a lot for evaluating a factual statement independently.

The one thing with this is that you have to be consciously careful of who you view as an authority on different subjects, or whose opinion on something is relevant. For a simple, everyday example, it's easy to follow a friend's recommendation to eat at a particular restaurant, even if that friend has completely different tastes in food than you do (which, in all likelihood, will result in a poor dining experience for you). Likewise, I think even smart, educated people often make the mistake of treating the word of powerful individuals as fact even if those individuals have absolutely no experience with or authority on the matter.