Difference between an estimate and a commitment

"A fundamental and common problem in many organizations is estimates and commitments are considered equivalent.”
—Mike Cohn
“Unless commitment is made, there are only promises and hopes; but no plans.”
—Peter F. Drucker

The difference between an estimate and a commitment seems simple: An estimate is an educated guess of how long it will take you to do something. It should not be thought of as a binding obligation. A commitment is an obligation to do what you say you will do.