How to Use "folly" with Example Sentences

1. So when depression economics prevails , prudence is folly .
2. Is this just a moment of collective folly , a wilful blindness to the lessons of the past ?
3. Would the american president still feel obliged to defend israel from the consequences of its own folly ?
4. But that would be utter folly .
5. Folly and ignorance play a part .