I think the best way is to try and treat happiness as a choice instead of at the mercy of ur brain juices. For example, saying I feel my body is getting stronger versus I'm tired and sore from that workout can have really positive impacts.

So in that way, when you're working towards success, you can define your journey as giving you happiness. And perhaps it might not truly be at first but it just might after a while.

To achieve it requires mindfulness; to be aware of your own thoughts.