What is the relation between fun and motivation? Are they the same?
As a temporary answer, and based on the comments, I will say that:

Motivation is related to the long term cost and revenue (in the broadest sense) for an activity, i.e. more extrinsic. If the long term revenue is higher than the cost, you might be motivated to undertake the activity.

Fun is related to the short term cost/revenue for an activity, i.e. intrinsic. If the short term revenue is high enough than a certain treshold you will say the activity is fun.

Improvements welcome :-)