It was Aristotole who first said that acting (imitation) is fun. The fun is why we act in the first place. I haven't heard of a single person who has said that he or she wants to become an actor because it is hard work. No, everyone agrees that acting is fun. Of course becoming a professional actor is hard work and doing an outstanding job of acting is hard work. But hard work that has a positive result is also fun.
Whenever an actor says he or she is nervous about auditions or has stage fright, one of the things I point out to them is that they are doing this because it is fun, so concentrate on that and the nerves and fear will subside. I tell them to use this mantra: "Acting is playing and playing is fun, whenever I act I am going to have fun."
Now, we mustn't concentrate so hard on having fun that we do not seriously approach any acting that we do. It isn't just a lark, It is a way to help make the production as good as it can be. Being fun does not mean that it is not important. Of course it is important. We always insist that anyone doing any acting work hard to do it well.
An advisee pointed out to me that the fun of acting should be part of the aspiring actor's motivation for continuing to attempt to be an actor, even in the face of the negative odds of succeeding because he or she can always act just for fun, even if acting for profit fails. This is related to ideas in my book, The Tao of Acting, in which I point out that an actor acts. It does not matter if the acting is professional or amateur. It only matters that the actor is acting in something. The fun of acting supercedes all other motives. It is something that you can do your whole life.