It's fun to do things just for fun.
Jon wants to advance in his career when his friend Bert asks him to go to an amusement park.
Jon wants to respond to Bert's invite.
Jon says that he will go to the amusement park with Bert.
Jon says he won't go to the amusement park because it's not work related.
Jon has a fun day which refreshes him and allows him to be more focused at work.
Jon will miss out on having a fun day with Bert.