I've seen this image floating around the web recently, supposedly quoting the Buddha. Of course, we probably cannot know if he ever said it, since the central texts about his life and teaching were not written until 400-500 years after he lived. (Unlike approximately 15 years for the earliest New Testament document, btw.) Regardless, what's your reaction to the quote?

believe nothing, no matter where you read it, or who said it, not even if I have said it, unless it agrees with your own reason, and your own common sense ~ buddha

In a sense, I agree with the quote. We of course should use reason and common sense.

But perhaps sometimes our own "common sense" is wrong. We sometimes develop bad ideas that need correction. If we rely upon our own "common sense" reasoning to decide whether an idea is true or false, won't we naturally dismiss any ideas that differ from our preconceived notions? After all, our "common sense" can often differ markedly from that of a similarly reasonable person standing beside us.

So I have written, for your kind consideration, my own statement on this issue:

That's just off the top of my head, maybe it's not much of an improvement. Then again, I didn't spend much time sitting around idly coming up with it. I guess the question comes down to in what sense we can really "know" things. The problem with the relativist viewpoint of truth is that no one actually can live consistently with the view that all truth is relative. What do you think?