'Period, end of story' is something a scientist can say—but it isn't science.

WSJ:

I felt nostalgic for those times when even the greatest scientific minds admitted limits to what they knew. And when they recognized well that the key to the scientific method is that it is a way of knowing in which you can never completely prove that something is absolutely true. Instead, the important idea about the method is that any statement, to be scientific, must be open to disproof, and a way of knowing how to disprove it exists.

Therefore, 'Period, end of story' is something a scientist can say—but it isn't science.

Absolute Certainty Is Not Scientific