Recently, two Scienceblogs bloggers have made substantive errors. (Well, no doubt more than two have, but I saw two.)
One is a mathematician and one is a biologist.
Now the fact that these writers made errors is of no great consequence. Every human, all of us, we all make mistakes. Everyone.
In fact, if some of us (well, okay, me) make lots and lots of mistakes. Actually, making mistakes is part of achieving anything at all, so we shouldn't fear making them (at least in situations where the consequences of error are not dire) - it means we're doing something.
What matters to me is not that they got something wrong, but how errors were dealt with. In both cases they made a post that pointed out they got it wrong, and that explained in detail what was correct.
A body of knowledge, whether it resides in an individual or in a culture, contains mistakes. Some of what we think is true is necessarily going to be false. If the fact that the corpus has errors in it is accepted, there is some hope of correcting some of the errors.
If you encounter someone who cannot be wrong, you may be sure they are in a sea of falsehood. It can be no other way.
However, we need more than just an acceptance of the possibility of falsehood and a willingness to change ideas. We can't just change our beliefs willy-nilly. The fact is, for most people, even the highly deluded among us, almost all of what we believe to be true is true, or close enough to true to be valuable (most of those truths are relatively mundane facts, it's what gets us through life). So we should need some further reason to change than the simple possibility we may be in error.
We need some way of identifying our most mistaken ideas and replacing them with better ones, without mistakenly replacing a good idea with a bad one. We need some kind of "filter" that allows us to see us to tell one from the other.
Some people use prayer to try to figure out what is right. The problem with that is it's mired in error. You can't tell for sure that what you think is divine guidance isn't just your own thoughts. In fact it's obvious this must be so, not least because two people can each be sure that they've received guidance about the right path, and those pieces of guidance are contradictory; since they can't both be right, at least one must be wrong. Whether you believe in God or not, the possibility that people can be mistaken in their interpretation of the result of a prayer for guidance should be obvious.
What is this magic knowledge-generating filter?
It's reason and evidence.
This is how we learn. This is how we discover what we did not know. This is why we even have a body of knowledge at all.
In order to raise ourselves out of the muck of ignorance, we need to admit the possibility of error, and use the only reasonably reliable filter available, in order to reduce those errors.