Joy and happiness are not necessarily the same thing. Most people spend their entire life in the pursuit of happiness. They seek a lifestyle that will give them comfort and satisfaction, which usually results in happiness and "fun". However, God calls us to be joyful, but not necessarily happy. And fun is typically a bi-product of doing what is right and isn't intended to be the primary goal. Joy is a result of contentment. Joy is a result of knowing that we are doing the right things and for the right reason. Happiness often is a result of our own desires being met. Joy comes from the knowledge of fulfilling God's calling for our life.
Lord, thank you that life is not supposed to be boring or void of fun but help me to seek joy in my life and not simply happiness or fun, which is often contingent on my situation while joy is an attitude that you have provided me.