For me, fun is fine when it occurs, but the key is to keep riding regardless. As they say, "when people ride bikes good things happen." Many of those things, in my experience, require frequency and consistency. Sometimes that is more work than fun and my body seems to respond best to riding five days a week. Everyone's goals are different. I'm not saying mine are better than anyone else's, but while I would love for every ride to be fun, they aren't and I'm riding anyway. Sometimes I hate this sport. Sometimes I love it. Crack addicts may have similar mood swings.