Smile

If you have seen the film "Batman - The dark Knight (2008)"
You must remember the actor "Heath Ledger" (The Joker)
In the film, there are two shots The Joker explain why his face like that
One is related to his father, another one is related to his ex-wife
This is the one related to his wife: (2:07 - 3:14)

"...You look nervous. Is it the scars? You wanna know how I got 'em? Come here. Look at me. So I had a wife. Beautiful, like you, who tells me I worry to much. Who tells me I ought to smile more. Who gambles and gets in deep with the sharks? One day they carve her face. We have no money for surgeries. She can't take it. I just wanna see her smile again. I just want her to know that I don't care about the scars! So, I stick a razor in my mouth and do this, to myself. And you know what? SHE CAN'T STAND THE SIGHT OF ME! She leaves. Now I see the funny side. Now I'm always smiling!..."

That's the one scars story of Joker
Maybe the story is Joker's imagination, not real
The story is really sad, but I can't fully understand what Joker's feeling
However I know what the feeling is now......
I'm the one who won't show my actually feeling in my face
So somehow I'm very sad, but I will show the smile in my face
As Joker said "Now I see the funny side. Now I'm always smiling!"
Cry inside, Smile outside

Why so serious!?!