God never promised we'd be happy. That's not to say we don't have moments of happiness, our first kiss, getting married, a child being born, etc. But happiness is fleeting, dependant upon external gratification and once the experience has passed we anxiously await the next thing that will make us happy. Besides who doesn't like feeling happy!? But like most feelings; happiness is short-lived and won't sustain in times of need. It's called the fruit of the Spirit not the feeling of the Spirit for a reason and happiness is not in that list.
A fruit seed is carefully chosen, patiently planted, lovingly tended, painstakingly cultivated and finally joyfully harvested. There's a process involved, knowing the season to plant and to harvest. And regardless of which fruit I'm growing it's not happiness that will sustain but contentment. As an added bonus it's godliness with contentment that is of great gain. Hm, who would have thought that throwing godliness into the mix would bring me into the realm of joy unspeakable and full of glory that trumps happiness.
Then I can say, as Paul did, "Not that I speak according to self-sufficiency; for I have learned to be content/satisfied in whatever circumstances I am. I know how to get along with humble means, and I also know how to live in prosperity; in any and every circumstance I have learned the secret of being filled and going hungry, both of having abundance and suffering need." (Phil 4:11-12) I no longer have to depend on being happy, happy, happy and self-sufficient but can know the secret of godly satisfaction; what could be better than that!