I'm not sure I'd have phrased it as "lies I've been telling myself", but I have a similar experience from a cross-cultural relationship, from mid 20s to early 50s. We had to work through conflicts more explicitly, with a lot more communication. Many things may be misunderstanding due to divergent assumptions, expectations, and even different body language signals.

I guess the "lie" exposed here is the way people can automatically believe they're seeing the truth of a social situation. It is easy to project false experience and motivation onto others. A more truthful approach recognizes windows of uncertainty around many encounters.

I think this applies to basic single-culture contexts too. Even in the same culture or the same family, we don't really know exactly what another person is experiencing.

Many seem cocksure that their social read is correct, and any grief is the other party's deliberate action. It takes a certain detachment to realize that your misreading of a situation may well be the genesis of a negative spiral, rather than a justified response...

The social aspect is a part of it, but it's just the tip of the iceberg. So much of how we fundamentally see the world- the role of the individual vs society, luck vs skill vs determination as being important for success, what defines a 'happy' life- is determined by our own conditioning. By seeing someone else's perspective you start to appreciate that there aren't many 'first principles' in life.

Take a simple example, marriage. If you're a Millennial you were probably brought up to think marriage is for love, and should produce kids. Depending on your orientation and enculturation, the wife is 'supposed' to stay at home or 'supposed' to have a career. We don't question the basic outlines of what a marriage looks like, unless you happen to be a part of the polyamory or fundamental religious communities, in which case you probably take those standards as being the ideal.

My husband's entire family had arranged marriages. Seeing their relationships gave me a new perspective on what a marriage can be, and forced us to be intentional about what parts of our culture we bring along. It's not that we're doing marriage 'better' than anyone else, but when you can't assume anything about what a marriage looks like you have to really examine it in detail.