Overestimation (noun)

1. The act of overestimating something or an instance of overestimating.
2. An excessive or exaggerated estimate of the value, size, or importance of something.

Origin:

From the verb 'overestimate' meaning 'to estimate something to be greater than it really is', which is derived from 'over' meaning 'more than' and 'estimate' meaning 'to judge the value, worth, or quality of something'. the term was first used in the early 19th century.

Examples:

1. The overestimation of the project's budget caused a financial strain on the company.
2. The overestimation of the crop yield led to surplus and waste.
3. The overestimation of his abilities led to disappointment and failure.
4. The overestimation of the size of the fish he caught was a common exaggeration among fishermen.
5. The overestimation of the value of the property resulted in a loss for the seller.