Let's accept it, crying is an avenue in which we release the tensions that are built within. It is a form of liberating pelt and suppressed emotions. This is but a natural reaction. Who would not agree when I say that it feels good to cry your heart out after each struggle or victory. Wikipedia says that crying is one of the three categories of tears, also referred to as weeping. Accordingly, crying or weeping "is increased lacrimation due to strong emotional stress, depression or physical pain". And it is not restricted to negative emotions; we also tend to cry when extremely happy or laughing.
Normally, goodbyes make me sad that I cannot help but cry. I would always say it is better to leave than be left behind. "Parting is such a sweet sorrow" as Shakespeare puts it. I guess not only does this refer to physical goodbyes, but also permanent goodbyes. Frankly, I also tend to shed tears for extremely dramatic films.
Some people would weep while praying, or trying to recall memorable experiences, and many other reasons. What makes you cry?



