Why in royal courts, were the fools the one ones who spoke the truth?

If a fool says 2+2=4, is it foolish to agree?
If a fool said the theater is on fire, would you at least check?
Why in royal courts, was the truth spoken sometimes only by the jester?

Now we call them conspiracy theorists. But who is really the fool?

The court jester image is from Public Domain, https://commons.wikimedia.org/w/index.php?curid=1760050