They don't, really I think.
Think of long term compliance and keeping a habit rather than motivation.
1. Inspiration. Like a brief, but high wave that rises quickly and falls quickly
2. Motivation. A less brief but less rapidly falling wave of excitement
3. Habit. A shallow, but long lasting wave
4. Enjoyment. A very high, and long lasting wave.
So firstly, its less wise to rely on inspiration and motivation, by their nature they will run out, you will do something for a short time, frantically, then it will fade and you cant spike inspiration or motivation again, so you stop.
Secondly, Enjoyment, that might be inherent, or it might come later, but assume it wont.
Habits then, are the key to long term compliance. If you are doing exercise, make it the gym (or a place). But ideally something you enjoy, but say its not something you enjoy, go somewhere, and set a reasonable schedule (monday, weds friday). Go at the same time every time. Don't miss a session unless you have to, and use inspiration and motivation to establish the habit. The same time, same place, same exact routine (do everything prep in the same order, they act as cues and will trigger the habit). Do the same routine for 2-4 weeks, without fail, use motivation, then it is moving and you have a habit.
Then, use motivation, or whatever else to keep yourself going. If you get injured, go anyway, because you are keeping up all the memory cues that keep the habit.
Finally as an aside, no, you wont ever look that cut. Realistic goals.
For me personally when I am in the gym routine I love it. Fall off the wagon, its hellish starting again.