There is a principle that makes you do this but it doesn’t say it the way your professor did. 

Every function orchestrates other functions. Even adding two numbers together and assigning them to a variable is orchestrating functions. You can twist yourself in knots thinking this way. 

[The single level of abstraction principle](https://8thlight.com/blog/javier-garc%C3%ADa/2019/06/11/refactoring-levels-of-abstraction.html) up holds the spirit of that idea but doesn’t require that you pretend you know where the bottom is. It only requires that you set a level of abstraction and stick with it. 

That means this is not structural. It’s conceptual. It doesn’t matter if you mix functions from your own code, a library, or even the basic language functions. 

What matters is that when you mix them together they don’t yo-yo your brain up to hand waving high abstraction and down to low level details all within the same function. 

Do that and you’ll end up *separating orchestrating and doing* just fine.