Fitness and money are easiest examples. For some, being fat is disguisting and unimaginable, so they will do everything possible to stay thinner. For some that threshold is having an actual six pack, and once you lose it, you go into emergency "at whatever cost" mode.
That's def the case for me with below average college-educated income - when I was below it, I was in "how can I be such a failure" mode. But now that I am above it, I am not in panic mode, even though I consider myself a failure, it's "good enough" on some "subconscious" level, despite me constantly trying to change it. Whereas if someone was born rich, I think not being able to keep up with the previous standards of life could be the threshold.
So, there are three take-aways from this. Once you establish a new height, you realize how good it is to be there and that it's possible, so you can get back there far easier. The second is that it's very easy to get lazy once you are comfortable. At that point you can also "afford a life", and that starts eating away your time. Edit: The last one is what the poster below said - maybe realizing how important these thresholds are is a key to artificially creating them.
Other than that - I think "focus on one thing at a time and set a concrete time block for it x days a week" is the vest possible strategy.