Overestimate (verb)

1. To estimate something as being greater than it actually is.
2. To have an excessively high opinion of someone or something.
3. To form a wrong judgment about the size, value, or importance of something.

Origin:

Late 19th century: from over- + estimate.

Examples:

1. He overestimated the value of the company's stock and lost a lot of money.
2. She overestimated her abilities and was unable to complete the project.
3. The team overestimated their chances of winning the championship.
4. He overestimated the impact of his new policy on the economy.
5. She overestimated the popularity of her new book and was disappointed with the sales.