The purpose of life is not to be happy. It is to be useful, to be honorable, to be compassionate, to have it make some difference that you have lived and lived well.
Sometimes we get sad about things and we don’t like to tell other people that we are sad about them. We like to keep it a secret. Or sometimes, we are sad but we really don’t know why we are sad, so we say we aren’t sad but we really are.