One life to live ...

There are a number of approaches we can take to the question:  what should we do?  What acts should we take, given that we have only one life to live?  What should we focus our attention on? This question is broader than the question of what makes us happy. Here are some approaches.

Determine what makes humans generally happy and fulfilled.  Do that.

 Figure out what makes you happy and fulfilled.   Do  that.

Figure out what makes others happy and fulfilled. Do that.

Determine worthwhile goals.  Figure out how best to reach them.   Do that. 

Figure out what is best for your community, tribe, or world.  Do that.

Figure out what is expected of you.  Do that.

These approaches are not exclusive,  but they offer different starting points.