Disagree. The cliche‘ is bandied about too frivolously.
What determines the value of something? How much you’re willing to give for it. The need could come for any of us to fight for those who matter to us, if we stand up for them, then we might truly validate this claim. The rest, to me, is just so much bluster.
Just seems like a lot of drama. I can't even think in those terms. If my husband (or anyone) doesn't want to be with me then it means to me he doesn't enjoy my company. So why would I want to fight for that? Or also if he was were with me just because I fought for him then seems I would have to just continue fighting for him and who has the energy? All of which is possibly what you are saying but if so then why mention fighting at all?
Disagree too. I think there may well be times when you do have to fight to save a relationship that can be worthwhile.. For instance, what if your partner were unwell, and going through a terrible time, fearing rejection because of their illness.. It may be worth putting in that extra effort there.. There are many other examples.. That said yes, there are times when putting effort in, especially if it happens on a repeated basis, just isn't worth it.
I think it depends on what the fight's about, and maybe the type of fight required.
For instance, if someone has a tendency to philander, I wouldn't fight about it; I'd end it. I wouldn't even discuss it. Trying to cling to someone like that is a recipe for misery, and trying to control them will only make them rebel and become more secretive. One can't force another person to change, and faithfulness is meaningless if it's not voluntary and sincere.
If someone developed a drug or gambling addiction, I'd be gone in a flash. I would stay and offer support only if he entered a 12 step program of his own accord. (And even then, I'd be skeptical. I prefer to avoid addictive types if possible.)
If a person wants to leave the relationship, I would usually just let them. Because I wouldn't want to be in a relationship that wasn't mutual. But if the reason for leaving was because of some unfulfilled need, and if it gave me pleasure to give in that way, I would. So "fighting" could happen in the form of working to replace a bad habit with a good one.
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If the fighting is about conflicts and problems in circumstances or within the relationship, then fighting is worthwhile - but "fighting" is the wrong word. It needs helps to find the right ways to listen and to communicate. For that, I like NVC.