Everyone seems to complain that in a relationship, it's futile to expect a person to change for you. So it is. But no one seems to acknowledge the logical underpinnings of why it is futile. It's looked at as just a leopard/spots situation, not amenable to reason: the person just can't change, and you are foolish to expect otherwise. Often there's a wistful, implied undertone that if only the person were more open to reason, (to "being reasonable") then they could change their spots. People aren't leopards, after all, and hope springs eternal (et cetera...)!
But the fact is, it isn't lack of openness to reason that prevents such change. The more one attempts to apply reason to the problem, the more one is forced to admit that the request for change is itself unreasonable.
Now to be clear, I'm not speaking of changes to behaviors that are self-destructive, or that otherwise clearly violate the spirit of a committed, exclusive relationship. Such behaviors certainly would be vulnerable to a reasoned critique, and can be argued against on merit. Depending on the leopard involved, you might even succeed in making your case!
But if the request for change is not grounded strongly in some external, mutually agreed-upon-as-valid moral or ethical principle ("mutually agreed" = by both parties in the relationship), then the request for change falls flat, in terms of justification. Such requests boil down to: you should change your preference, because of my preference. Can such a request be substantiated? Let's set some terms.
Say Person A and Person B are in a love relationship, a committed and exclusive one. Let's say Person A wants Person B to change, in some way for which external moral or ethical justification is not available. Let's say Persons A and B have agreed that each others' feelings and wants matter.
Obviously, if they had agreed between them that what Person A wants is all that matters, than the requested change could not even be an issue: it goes, because what Person A says goes. But such is not generally the case. It is customary in love relationships for the dynamic of wants and needs to cut both ways. In such a relationship, how can Person A validate a claim that Person B should change, despite Person B's preference not to change? If we agree that what each person wants matters, and that what one person wants is not worth more than what the other person wants, than there seems to be no justification for Person A's preference to override Person B's preference.
Certainly the oft-heard plaint: "It's such a small thing, can't you do it for me?" makes little sense in this context. If it is indeed a small thing, then Person A can be expected to overlook it more readily than Person B can be expected to change it.
Person A is free to claim that their desire for Person B to change is greater than Person B's desire to remain unchanged, but this claim seems questionable on the face of it: what unit of measure is being employed?
The statement: "You would change this for me if you loved me," is likewise suspect. It appears at its core to be a very dubious sort of syllogism. Person A is reasoning that Either:
1. People who love me do whatever I say,
2. You love me,
3. You will do whatever I say!
Or, the implied threat of the negation:
1. People who love me do whatever I say,
2. You won't do whatever I say,
3. You don't love me.
In either case, the major premise ("1. People who love me do whatever I say,") seems very far from a healthy assertion to make, in the context of a relationship between equals.
In the final analysis, absent a successful appeal to some external agreed-upon and decisive principle, any call for change must be considered as based primarily on personal preference. Expecting the one you love to change based on your preference is an inherently unreasonable stance, rooted in an assumed imbalance in the relationship. On some level you are assuming that what you want is more important than what the other person wants. A call for the other person to exercise self-sacrifice rebounds instantly upon you with an implicit charge of hypocrisy: if self-sacrifice is required, why are you not the one being called upon to exercise it?
In the absence of meaningful quantifiers by which to gauge relative degrees of intensity of preference between one person and another, and in view of the general principle that neither person should expect their preference to outweigh the other person's preference, it does not seem possible for Person A to claim that it is more reasonable for Person B to change the behavior in question, than it is for Person A to overlook the behavior in question.
In closing, it is not the unreasonable refusal to change, but the unreasonable expectation of change that destroys harmony and undermines respect and cooperation in a relationship between equals. Once the basic truth of the above is acknowledged, and the unreasonable expectation of change based on an implicitly imbalanced hierarchy of desires is removed, it is usually possible for the two parties to proceed in a clear-eyed and reasonable fashion towards an amicable and mutually-satisfactory negotiated solution.