Maimonides

If a person studies too much and exhausts his reflective powers, he will be confused, and will not be able to apprehend even that which had been within the power of his apprehension. For the powers of the body are all alike in this respect.

But if, on the other hand, we should be justified in rejecting it, if there testified on oath, then, supposing our rules of evidence to be sound, we may be excused if we hesitate elsewhere to give it credence.