well, not sure about others, but for myself, I know what makes me happy after paying attention to my feelings I have after doing various stuff and reflecting on the circumstances in which I have had them. I do it pretty often.

Sometimes, though, I do fall into a trap of mixing up causality and correlation.

I may feel happy after talking to someone... and only after concluding a thorough analysis of my feeling and the timeline, I may realize that the fact of _finishing_ the talk with that person makes me happy and not the talk itself 8-( )