Underestimate (verb)

1. Form a less favorable opinion of (someone or something) than is deserved.
2. Judge (something) to be smaller, weaker, less important, etc. than it really is.

Origin:

Late 19th century: from under- (expressing undervaluation) + estimate.

Examples:

1. You should not underestimate the difficulty of the exam.
2. She underestimated the strength of her opponent and was quickly defeated.
3. The company underestimated the demand for its new product and struggled to keep up.
4. The politician underestimated the intelligence of the voters and was not re-elected.
5. The team underestimated their opponents and was easily beaten in the game.