noun
1. use of poor judgment, or lack of common sense.
The problem was caused by my own folly, and I am solely to blame.
2. an act or acts of foolishness; rash behavior.
He is now suffering the consequences of his folly.
3. an unwise or foolish undertaking, such as an expensive project that fails.
Investing all his money in a risky scheme like that was sheer folly.