Happiness needs to be experienced. Explaining what it is or how it feels is of low value. The problem is that happiness is directly linked to unhappiness. It's like notes and pauses: if we remove pauses from a melody, the melody turns into a "sound" that doesn't give us any pleasure.. it's not music.
So to experience happiness, we need to experience unhappiness for long stretches of time.
All this to say that happiness shouldn't be the end-goal IMO. Meaning makes more sense as an end-goal. If we can live "meaningful" lives, happiness could be a byproduct. Being happy is easy but transient (e.g. eating ice-cream can make someone happy). Finding "meaning" is difficult but way more permanent than "happiness".
I would separate career from "meaning" though. The two rarely go along and I also like to think that myself and everyone else is more than a "career".