Do not do this. Do not live in the past. Do not think about what might, what could, what should have happened. Learn from it and move onwards. Nothing good comes from constantly dwelling on things that can't be changed.
A better bit of advice is "avoid ruminating" and this applies to every thought, not just the ones that involve the past. But even that is not easy, especially for those who create things, since to create something you have to ruminate on it heavily, for months or years -- this is probably why there is an overlap between depression and creativity.
Self-reflection seems like rumination, but the goal is to learn something from whatever you're examining. To take a lesson from it, if there is a lesson. Not every moment is a teachable moment. If you're lucky, many of them are.
Sometimes an experience is just an experience, and there's nothing different you could or should have done. Take, for example, the numerous times I've been honked at in traffic. Is there some hidden meaning in those beeps? Should I have been paying more attention in that moment? Or did I make an honest mistake? If it's an honest mistake, there's nothing I can really do. No magical training regimen will make me an infallible driver, so I have to move on.
It's tempting in some cases to keep looking for a lesson. Some experiences will never contain a lesson no matter how hard you look. Rumination is cultivating the desert of those experiences.
The fundamental activity involves reviewing a thought over and over again, sometimes thousands of times over many years. Sometimes this leads to a new painting, a new novel, a new movie script, a new piece of software, or a new insight about something that happened to you as a child. Sometimes a person fails to make any progress.
You write "The key difference" but these are words without meaning. Sometimes you ruminate on a novel you are writing, but you can't figure out the ending, so you accomplish nothing. Sometimes you ruminate on that time you insulted your alcoholic brother and the next month he killed himself, but this time, reviewing the memory, you recall that he'd said he was going to kill himself long before, so it wasn't really your fault.
There is a reason why therapists often want to talk about a person's childhood -- sometimes reviewing the past leads to a new insight. Sometimes it doesn't. You can't judge the value of the activity simply by whether it produces something. Sometimes it will and sometimes it won't.
Thinking about something briefly and then moving on cold turkey is often completely phony: basically a form of denial. You're not free if you have "off limits" areas that you don't let yourself think about.
Maybe sometimes it’s abjectly true - you became homeless and in the past you weren’t so it was better back then. In a lot of cases you’re probably looking back on a high moment while in the middle of a low moment. Either way, the comparison does far more harm than good and it might well hold you back.