If you are certain of something, then you should hold the truth of that thing regardless the evidence presented against it. To do so would be irrational.
Yet if you hold to a theory when the evidence disproves it, you are also irrational.
Therefore, it is irrational to be certain of anything.
QED
Yet if you hold to a theory when the evidence disproves it, you are also irrational.
Therefore, it is irrational to be certain of anything.
QED