When do you sigh? Why do you sigh?
You might sigh when you're tired, frustrated, or relieved. 

But you might never know that sighing keeps us alive.

Sighing is a kind of survival mechanism- a thing we do without thinking in order to survive. 

Sighing also resets the lungs- I have to say, it makes us feel that our lungs more clear.

And we have to keep sighing in order to survive : I almost sighed about 15 times until I finished this paragraph. 

It's just an unchangeable thing, I think. it brings us some effects- Like relieving! 

Did you see how sighing effects our body?