Life is not perfect. Human especially, flaws are everywhere.
Sometimes, you're up, but most of the time you're always in the middle or down. So you fake a smile when people ask you 'How are you today?' and pretend that life is great like a perfect non-bubbled sunny-side up. Nobody knows and you don't want anybody to know how sometimes it's not even worth it to fake that smile.
But you have to.
Because life is not perfect. If it is, then you won't even know what's the meaning of life. What is the reason to smile. So when a little sense of perfections like a nice chat with your crush or a praise from your boss, you will appreciate life.
That is why God gave human soul. Emotion.
And He only give it to the strongest among the strongest, because he know that only those souls are capable and strong enough to face life itself.