It was his slightest folly.
He realised his folly.
He repented of his folly.
He has admited his folly.
I committed the folly of trusting you.
It is an act of extreme folly.
You have to apologise for your folly.
You must realise your folly and complete the task.
I am sure one day you will realise your folly.
Anger begins in folly and ends in repentance.
He realised his folly and was filled with remorse.
It is a folly to fight in the name of religion.
You have to pay a heavy price for your folly.