What I tell them is that writing isn’t like math. In math, if I said 2 + 2 = 5, then I’m wrong and I need to fix the mistake. But in writing, there is no right or wrong, and a rough draft is an important first step.
Revision is about improvement. It’s about taking something that’s okay and making it extraordinary. A first draft is important because you can’t improve something that doesn’t exist
And then I tell them that, for me, revising a manuscript is like renovating a home. This is a comparison they really seem to get.