If applying this to poly, I'd be thinking more widely. Relationships don't just start and then end. You need to pay attention to what is going on while they are happening and adjust them as you are going on. I suspect poly folks are fairly good at doing this on the whole.
Also - it is not simply a person's own requirements that they should pay attention to. The requirements of the others are just as relevant. You've outlined paying attention to that very clearly in your previous post.
Also - before you even start, assessing where you are is good. Somebody who is good with people and part of a community where poly is widely practised is in a very different place than somebody who has been married to the same person since they were 20, has lost or never had good skills with people, who's spouse doesn't like the idea of non-monogamy, who is parenting a couple of small children and works a full time job.
That sort of thing I think if you were to apply it to poly. I'll think about it some more and see if I can come up with anything else. It's an interesting question.
Re requirements. I was more thinking of it from another perspective. Say, for instance, you might require someone single, because you want them to be able to see you often without too many distractions. Then, you have a relationship with a single person and the difficulties of trying to accommodate a secondary relationship with someone who would prefer to be your primary become apparent. The relationship consequently ends. Next time, you need to adjust your own requirement for a single person because it's obvious it doesn't work for you and causes trauma to all involved.