I'm not sure it's attainable. Even the founding fathers spoke of having a right to the PURSUIT of happiness. And maybe that's what makes us happy is in the pursuing of it.
Or maybe it is . . . The Merrian-Webster website says the first definition of happy is a "feeling pleasure and enjoyment because of your life, situation, etc." I think I got that . . .
Is my "happy" under my control? Completely.
I get to do the choosing. I get to decide to experience enjoyment regarding my situation.
And if I'm not I'd better choose a different situation!