There are a lot of good thoughts here but I'd like to share my two cents.
I want to preface this by saying I started lifting 30+ years ago. I still squat in the 600's and bench in the 400's and my profile pics speak for themselves. My point is that I'm very familiar with the gym.
Sure, I love training. But after so many years, what's my goal? Answer: Currently, I don't really have one. Training is just what I do.
If I feel great, I show up. If I feel not-so-great, I show up. If I feel bad enough, I take the day off and start with a blank slate next time. No need to try and make up for lost time.
If I don't feel so good, I do a few warm-up sets and call it a day. Other days, I get a little excited a set a PR.
If I have a contest or something coming up, motivation comes into play. If I don't, then motivation doesn't exist. Only habits. And over time, habits create results.
I don't even like using the word discipline because it implies forcing yourself to do something. But habits? You do those without even realizing it. And if you don't do them, something feels off.