"They must often change, who would be constant in happiness or wisdom."
Change. Most change doesn't happen overnight. It's a gradual thing. Whether you want it to happen or not - change is inevitably going to take place.
Right now, I am looking forward to change. I'm working on making some changes happen - and it's not an instantaneous. Changing habits, lifestyles - those take time to grab hold. You do eventually come to realize that it's no longer work. That change you were trying to make is made. But then a time will come when I'll need to change something else. That is - according to Confuscius - if you want to be happy & wise, change is something you must do often.
So I'll continue to work on the changes that I've begun. When I hit a bump in the road or make a step backwards, I'll focus on the forward motion - the progress I've made. And then one day I'll wake up & realize that the changes I'm trying to make are done; the new habits are formed & I'm happy - maybe even a bit wiser.
At least for a while until the next change is needed. Because I also read "when you're through changing, you're through" and I'm not quite ready to be through with life yet. So I'm going to continue to try and embrace change.