My friend Mike happens to be a history major at university. As he has progressed through school, he has come to the conclusion that it can be very hard to verifiably prove a lot of things in his area of study. Ancient history in particular has little first-hand evidence and the evidence that is available tends to be rather biased. As a result, Mike has found that skepticism is a necessary response to initial information because the initial information is so often unverifiable, wrong, skewed or incomplete.
I have been employed as a computer programmer for more than five years now. One of the trickier aspects of my job is to determine the source of software bugs that are automatically reported for our software. Sometimes an error is immediately obvious, perhaps due to a spelling mistake in the code. Sometimes an error becomes my personal nemesis, mocking me as I spent hours or even days trying to reproduce and solve it. I once had an error that took me three months to solve as I revisited it every week or three as it was sporadically reported. In cases like these, the evidence that I have to use is circumstantial at best and hopelessly misleading at worst.
As a result, I have honed a rather specialized skill in hunting down bugs based on little evidence or bad evidence. I often have to make large leaps of logic during this process or I have to ignore bad evidence altogether. More often than not I eventually prove my conclusion correct after the fact, in that I duplicate and fix the bug.
I think it's interesting to see how our respective experiences have coloured how we both approach other areas in our lives that do not fall under our scholastic or professional domains. I consider Mike to be one of the great skeptics that I know, known to intially doubt anything from personal testimony to empirical evidence to his own conclusions. It's rather impresssive in it's own way, and quite consistant. Not to say that he naively disregards different kinds of evidence, not at all. Even if he approaches much of ancient history as a skeptic, he still knows more about it than most anyone I know. He just has an underlying precept that evidence isn't usually that good in many areas and for many reasons, and that conclusions drawn from faulty evidence tend to be faulty conclusions.
On the other hand, my general precept suggests that faulty evidence does not have to lead to faulty conclusions, if used properly. The reported bugs in my software most likely have a reasonable cause that can be found, even if the related information is entirely misleading or if the error cannot be duplicated reliabily. Even if the evidence is irretrievably flawed in some way, the conclusion may still be correct regardless. As with Mike, this approach doesn't dictate my decisions or conclusions. It's merely a common thread that I see.
So Mike and I agree completely: Evidence and arguments of all kinds can be highly suspect for numerous reasons. Part of the purpose of the principles of critical thought is test our own thoughts because we can't always trust them due to our potential biases, emotions or other factors.
The difference between us is that Mike prefers to defer a conclusion until good evidence is available, and will otherwise try not to make a conclusive decision based on poor or incomplete evidence. (As I said, this can be very admirable.) I do not think that poor or incomplete evidence necessitates avoiding a conclusion, though it certainly discourages it.
Some historians will look at ancient history as if through clouded glass, doubting the faint images that they can see through it. Other historians look at ancient history as a puzzle. You can take the pieces and form an accurate picture, even if some of the pieces are missing or are from entirely different puzzles. I would be the second kind of historian.