A couple weeks ago Bill Nye and Ken Ham had a debate about creationism. Of course, nearly every point Ham made was factually inaccurate. But beyond having the simple facts wrong, Ham also had a fundamental misunderstanding about the nature of evidence.
This was highlighted most clearly in Ham's answer to the question "What could change your mind?". His answer was, summarized, "Nothing". Now, this answer in and of itself is a serious strike against Ham's rationality. The point of changing your mind is to make your beliefs more accurate. If you don't even admit the possibility of changing your mind, you're saying that your beliefs cannot possibly be wrong, which is, well, arrogant to say the least.
But it's worse than just that. Ham also said that the Bible makes testable predictions. Alone, that's not a bad thing, quite the opposite. But when combined with his statement that nothing could change his mind, it shows that he doesn't understand the point of predictions. The point of predictions is to provide evidence, but the thing is, that evidence can go either way.
If you make a prediction and perform a test, and the results of the test match the prediction, then that is evidence that supports your beliefs. On the other hand, if you make a prediction, and perform a test, and the results don't match the prediction, then that is evidence that opposes your beliefs. If there is no such outcome that would go against your prediction, then it's not a prediction at all.
For example, suppose I held a rock, and based on my beliefs about the material it's made of, and the laws of physics, I predicted that when I let it go, it would fall down. Then, if I dropped it, and it fell down, that would be evidence in support of my beliefs. But, if I dropped it, and it didn't fall down, either falling up, or hovering in place, or anything else, that would be evidence opposing my beliefs. If I had predicted that when I let it go, either it would fall down, or it wouldn't, then I haven't actually made a prediction. I haven't, in any way, specified what the result of a test would be, which means no outcome can oppose my beliefs, but no outcome can support them either.
If Ham thinks the Bible really does make predictions, then those predictions failing to come true should change his mind. If nothing could change his mind, then his predictions can't actually provide evidence.