Not every sky will be blue and not every day is springtime. So on the spiritual path a person learns to find this kind of happiness without needing nice things to happen on the outside. Rather, you find happiness by being who you really are. This isn't mystical. Young children are happy being who they are. The trick is to regain such a state when you are grown and have seen the light and dark sides of life.
The activity of the immature human being is simply played upon to secure habits which are useful. He is trained like an animal rather than educated like a human being. His instincts remain attached to their original objects of pain or pleasure. But to get happiness or to avoid the pain of failure he has to act in a way agreeable to others.