'I’m not a designer, but...' and other things that will ruin a great idea

My hiring goal, as a general rule, is to make myself the dumbest person in the room. There are tons of people who have recognized this and have stated it more eloquently than myself. For illustrative purposes, I’ll quote Malcolm Forbes who said, “never hire someone who knows less than you do about what [they’re] hired to do.”
It just makes sense, right? Why pay someone to do something that you’re already great at? On its face, it seems so logical -- so infallible --