Believe it or not introduces something surprising but true. Believe it or not, he walked the whole way.
It warns the listener not to dismiss what is coming, which is a small claim of honesty. It sits at the front of the sentence and can be moved to the end for effect.
1phrasebelieve it or notIntroducing something surprising but true.
“Believe it or not, the shop is older than the town hall.”
believe it or not is a phrase.
Practised in Small Talk & Everyday Phrases