One partner has one definition of the nature of reality, purpose in life, goals in life, direction in life.
The other partner has very different views.
One example is when one partner is on a spiritual path, their whole goal in life to expand in consciousness, and the other partner's goals are to succeed at work and attain material things.
You can't change a person's values.
Who they are, what's important to them, their goals and ambitions are exactly the path that they should be on. It's right for them. It's a path where they can best learn what they came here to learn.
To argue values, to argue paths is futile. There can be no compromise. Because each compromise is a major sacrifice of values for the person. And that's not a compromise.
My recommendation for a harmonious relationship is to aim to meet someone who shares your values and goals.
When the couple shares values it's easy to negotiate difficult situations because their aims are the same. Compromise is not about giving up values.
If you're struggling in your relationship with no apparent way out, maybe you need to think about your values and take appropriate action from there.