"The successful person has developed the habit of doing things failures don't like to do. They don't like doing them either necessarily. But their disliking is subordinated to their strength of purpose." Albert E.N. Gray
I don't necessarily agree with the line, "exercise should be fun." In my world, I see exercise as a means to an end. I guess exercise can be fun. If you are showing up to a gym and have more interest in spending time with your friends and sweating a little, that could be fun. But training is not fun. It can be enjoyable, but not fun. There are those who enjoy constantly challenging themselves to get a little better every time they train, there is enjoyment in that struggle.
I guess my point is, don't set goals with the expectations of the process being fun. Nothing that's worth anything is that fun to get to. These days, there are many exercise programs marketed as being fun. Its more about feeling good than accomplishing your goals, and that's okay for a lot of people. I tend to think accomplishment is more fun. There's nothing like standing at the end of your struggle, appreciating all the things you did that sucked to reach a brand new you.