I agree that interface is key to not just software design, but design in general. Designing parts in isolation, you can do pretty much whatever you want. But people being able to gracefully handle where and when two parts collide is what makes the software world go round. One of my favorite bits on interfaces is this Rust Koan[0], which has a funny twist of pragmatism at the end.
It's a shame too many developers think this huge idea is just the interface keyword, or OOP, or even just the `object.method()` syntax. I hear dot-autocomplete come up in conversation almost every day now. When I was in college people asked me "How can you even use C? It doesn't even have classes...?", the implication being you couldn't encapsulate your code at all, and I get the same shrinking feeling when people talk about dot-autocomplete as if it's synonymous with interface discoverability. But it's really just one particular implementation (heh) of a much broader and more abstract (heh) idea. It's like calling all tissues Kleenex or all sodas Coke.