The problem isn't the word "simple" it's words like "just". Within something complex, there can be a simple thread of reasoning that may not be easy to see and

The problem isn't the word "simple" it's words like "just". Within something complex, there can be a simple thread of reasoning that may not be easy to see and once communicated, everything takes shape and begins to make sense. That's worth communicating even if it's not easy to describe. Often that may be how the author came about the design. I wouldn't know how better to describe such a thing. Explaining all the complicated things that make the simple thing work ends up with the reader being able to agree with all the explanations, then wonder "yeah, but why do those all add up to do what it does?" Tone of writing is important, but also a reader shouldn't assume that something that has a simple core is easy to make or later understand. I'd say it's more constructive to have your docs show how/why it's simple rather than make a statement and leave it up to the reader to piece it together. What's a better word than "simple" that doesn't make it also imply "easy" to many? e.g. the elevator thought experiments of General Relativity are simple, but not easy to come up with or initially reconcile.