In a trial, or in a scholarly investigation, you can't know the answer ahead of time. You have to have things play out at they will. That's why you can't be too invested in a certain result before that result is demonstrated. It can be difficult because the original purpose of our scholarship might be to prove certain things. I would submit, though, that the truth is usually more interesting than the preconceived prejudice.
In humanism, of course, we have many prejudices, and we want them to be true. Usually, we can prove our points, because our disciplines aren't objective in the first place. We don't have data, but rather cherry-pick our examples to prove what we had in mind in the first place. Even here, though, I would say that we should be open to being proven wrong. I think our results will be more interesting that way.