When one or the other stops compromising. There are always differences between people. Extreme differences mean a lot more communicating rather than letting tensions build.

As long as differences are not an antithesis of each other, they may give an added dimension to each other.

I definitely do not think a relationship between a religious person and an atheist would work. I don't think opposites attract. I think doing things together and being on the same page. works.

Also even couples who have everything in common with respect to existential philosophical positions can fail. I’d rather be with a selfless Christian (as long as he or she isn’t a fundamentalist) than a selfish or hedonistic atheist.

There are the differences that add spice to the relationship and the existential philosophy differences. I think relationships can work with both but couples with the latter need to think long and hard before they add kids to the mix.

I have no idea. I don't think in that paradigm-I think in terms of complementary/harmonious. I'm not sure how I would even relate to someone very different than I.

When the opposing positions outweigh the positives associated with the relationship. For me, I knew it was over when my ex let it be known how bigoted she really was towards homosexuals. This was, at the time, an indirect attack against my eldest daughter, (she was my second wife and we have no children together). This made the continuance of a relationship untenable. This was really confusing when considering she has no problem with being bisexual as she is.

I think the degree of the differences is what matters. You obviously don't want and shouldn't want to be with someone that is so damn opposite that you won't understand each other, and dating someone way too similar to you basically reduces the chances of growing and evolving as a person because you're not learning anything new.

I think that the opposites attract thing is only for electric charge, not for relationships. I think major differences in core beliefs will over time doom any relationship with significant differences. I think that there is little that can be done to prevent growing apart in such a situation.

When you find you don't have enough in common to stay connected.

I had a girlfriend say " we were not equally yoked " and that comment came into more conversations till there were no more conversations to be had, we broke up.

If a couple can't decide where to eat, they should just call it quits right there and then.
Facts.

no person is truly your opposite. claiming opposites attract is a scapegoat for, "I choose lust over compatibility and blame it on an age old anecdote."

Depends on how important the differences are and how rooted you are in your belief. My wife and I are polar opposites in almost EVERY way, but rather than harboring resentment over our differences, we often find ways to learn from each other and grow as individuals. We respect each others individuality and love each other FOR our differences rather than in spite of them.

It depends on how opposite. If he likes chocolate and I like vanilla, if he likes the color blue and I like red, I have no problem. Those are silly differences. When I met my ex we both liked different brands of coffee. He stated that we would buy mine. My answer was that we would buy both. Things like that can build resentments. These things may sound trivial, but it is important to respect the other person for their likes and dislikes, and then to try and accommodate each other. If you have different hobbies, it is important to respect that. Of course, you hope to share activities and hobbies as much as possible, but if he loves to go to football games and I hate it, there is no sense in putting us both through a bad time of me squirming during a game, wanting to go home, and him being uncomfortable because he knows I don't want to be there. I say go with your friends, enjoy, and we will do something alter that we both like. Again, may sound trivial, but it really isn't. Opposite personalities. Having been a teacher of children with disabilities, I've learned a lot through the years about personalities and learning styles. It is important to learn that you both can approach something in different ways and allow for that. Where I see no compromise would be if he is a right wing religionists and I am a left wing atheist. How do cuddle on the couch and watch TV while he praise Orange Nazi Trump? I've tried in the past with guys who had opposite values in politics and religion. It never works because these views are indicative of who you are as a person.

I should be able to answer this, since my ex and I were quite opposite. I think as long as both parties are still intrigued by the differences and interesting in sharing in them and learning from them, then the 'ship can last. My ex, by her own words, was selfish, and it seems uninterested in learning from my perspective. I'm always the learning type, and always fascinated by the different ways human minds can work, and that discord is why we didn't work.