The antonyms of the word "over-estimates" are "under-estimates" or "under-values". When we over-estimate, we exaggerate the value, importance, or ability of something or someone beyond its actual worth. On the other hand, under-estimation means undervaluing or underestimating something or someone with less credit or lower importance than it deserves. In real-life situations, over-estimation may lead to disappointment, while under-estimation may cause missed opportunities. Therefore, it is essential to find the right balance between the two to make informed decisions and have realistic expectations.