I heard a quote a while back, can't remember wherefrom, that has become quite significant to me. It was ''anything worth doing is worth doing poorly.'' I personally feel the intense roller coaster ebb and flow of motivation and apathy, and when it's good, it's *good*, but when the motivation goes, everything stops. Or at least it has in the past. I've felt like if I wasn't doing the best that I could do, it wasn't worth it, so I skip one day, then another, and so on.
I personally get carried away in the programming, strategy, etc. and what gets lost is that before you can do anything, you must first resolve to do something. This resolution has to happen on a daily basis. So long as you are doing something, I think you'll find that you'll make progress, even if only a little. And that progress helps you find the motivation again, after which you can go crazy.
I don't actually think that much separates the successful from the unsuccessful in terms of what they do when they're motivated, when they're feeling good, when that urge returns. I think it's mostly what they do when it leaves. They just keep going, and they do *something*.
Last year I learned Finnish. I did my YKI test 1 year after I arrived in Finland, and was rated at a B2 level in speaking. How I got there wasn't by being motivated all the time. The motivation left after 3 months lol. I just kept going. Whether that was reading one single page, or listening to the news in the car, or talking to someone at the park. Now I'm taking that approach with fitness. I don't have a program. What I have is an agreement with myself: no matter what, I lift 3 times per week. Some weeks are awesome, and I am a beast in the gym. Some weeks are a struggle, and it's more that I kept a promise to myself, and gave whatever I had on that day. Going 4 months now, and I feel great, not going to stop any time soon.