What is a happy ending? Laughing yourself to death? Dying of a heroin overdose?
Why would anyone want that?
And if you use the more traditional interpretation: you live happily ever after… why would you think the world works like that?
Life only has one definite ending, and it’s probably not going to be happy.
So you need to make your own happiness… You need to be willing to endure short-term pain and suffering to achieve long(er) term happiness…