Underestimation, to make too low an estimate of the quantity, degree, or worth of anything, usually. Majorly in many things we make this kinds of mistake, of assuming things without knowing it properly, without finding out deeply, we come to a hasty decision, and make wrong impressions about those things, like any project, task, organisations, etc.
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Same way, we tend to figure out people also, we Underestimate people by their body language, personality, nature, some people are introvert, some are extrovert, shy, etc. And only by those outer qualities we cannot judge them, but we do!! We always do this mistake we judge them. Without knowing them properly, without coming in contact with the people, we just give decisions, those decisions taken are 90% wrong, for which we regret also later.
So we should not do this mistake of Underestimating things / people / anything….