Any good rule of thumb like the one in GP's comment is wrong sometimes, and that's ok. Adding more caveats just dilutes it without ever really making it watertight (if you'll forgive the very mixed metaphor).

But even in complex applications, there's still truth to the idea that your code will get simpler over time. Mostly because you might come up with better abstractions so that at least the complex bit is more isolated from the rest of the logic. That way, each chunk of code is individually easier to understand, as is the relationship between them, even if the overall complexity is actually higher.