I think it differs in the intent and in the span of it. The "pursuit of happiness" to me involves a validation of something (yourself usually) and that's the main difference, I believe that validation currently can't be helped no matter what we do, so when encountered it's best to question it, to challenge it and usually find out that we have nothing to validate.

Also when I talk about working to better ourselves it's not to become paragons of virtue or even version of ourselves which would satisfy us but to just try to offer a chance to be useful (and not to others now but like I said above as an almost useless nudge in a better direction), also to maybe through sharing an ability for what has been learned to be passed on (even to be denied later on) so that maybe one day someone doesn't have to restart from scratch when considering the questions "who am I, why do I feel this way, why do I act this way,..."

The real intent is also important because you can be a human scum inside who still spends his time helping other humans (because it make them feel important, because they relish in other people's misery, because they feel obliged to, because you do it for validation of others or for the show, or to lower your taxes or whatever the reason,...), that's why I am mostly talking about the mind in here and not the actions (although one influences the other). Usually we are not really aware of our own intents, at least not past the obvious layer. Maybe if we go to the source we will know how to avoid some behaviors (for us and others but the "we" means humans more than me and people who read this ;))

I don't remember where I saw this: "Happiness is already there", which expresses quite well which can be heartbreaking because it does not wait for you, it does need you to acknowledge it, there is nothing to pursue, the ingredients are all around you, it's only our sate of mind who will decide if you feel it or not. I am not sure it's usefull to give energy into what could be rather than what is. Especially if the former implies ignoring the later.

But then I am not saying I follow my own principles, I just consider I should.