Tears
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Tears are secretions from the lacrimal glands in the eye. They are generated due to a variety of mental or physical issues which may or may not be controllable by the individuals themselves.
From a mental standpoint, we cry either when we are distressed about something or our happiness knows no bounds. Loosing your girlfriend, getting your dream job, failing in the exam, losing an important deal, meeting your parents after many years and so on and so forth are the kind of situations which we all go through day in and day out.