The pursuit of happiness will be futile if it is happiness itself which is being sought. Happiness can only be experienced as a fruit of seeking after that which endures.
Sammy Rhodes writes about modern relationships and the reasons they founder:

Wanting happiness isn’t a bad thing. It’s a human thing. The problem is that happiness is less something we can directly seek than it is a by-product of seeking the right things in the right ways. Happiness is like the endorphins that flow after a good workout. They’re a result of hunting another goal, not something you can get your hands on directly. They only come by working out. Or so I hear. I’m less a work-out guy, more a work—in guy. And by that I mean most days I like to work on getting an entire bag of chips inside me.
Jesus told us to “seek first the kingdom of God and his’ righteousness, and all these things will be added to you” (Matt. 6:33). Blessings, like happiness, come as we focus our eyes on something other than those blessings. Jesus is teaching us here to think less like consumers and more like himself a covenant—making and covenant—keeping God. If Jesus had let happiness determine his choices, the cross would have never happened. Jesus’ choices were driven by his covenant promises, first to God, then to us.

Sammy Rhodes, This Is Awkward, Thomas Nelson, 2016, pgs 93-94.