Modern equivalent: don't text or email when you can call, don't call when you can speak face to face, don't speak face to face if you can wink

you see powerful people following this advice all the time, like with Bill Clinton and Loretta Lynch’s tarmac meeting. He flew in a plane to talk face to face just to ensure it wouldn't get recorded.

Don't set a meeting when you can email, don't email when you can slack, don't slack when you can do a :thumbsup: emoji one someone else's comment

If you know the original source I'd be curious to hear it.