I had to learn this the hard way. Almost everything I owned was destroyed in a flood a couple of years ago. I watched one of my housemates freak out and cry for days about it. It couldn't have been shoved in my face harder that the choice was mine. I could assume that happiness came from the lifestyle I designed for myself, as my housemate did, and therefore it had just been completely destroyed with no hope of coming back any time soon. Or, I could assume happiness was a state of being that could be achieved at any point in time, no matter what was going on: that there are no prerequisites to happiness.
And suddenly, I was happy.
And then I met my wife. And I got to more work that I loved, rather than needed. And found a modicum of success in my consultancy. And got out of debt. And made a lot of new, wonderful friends. After years of being unhappy and getting nowhere on the goals that I thought would make me happy, I flipped a switch and found out that the goals required happiness out of me.