Thinking is allowed. Judging is not.
Campbell never uses the phrase monkey mind. His image is an unruly two-year-old — and the instruction that follows from it is not to argue with the child but to tell it to sit down and be quiet until you are done.
What makes this usable is a distinction he draws that most meditation instruction blurs. Asked how you can give yourself direction without thinking, his answer is that you can think, as long as you do not analyse, judge, assess or compare. Giving yourself a direction — go there, stay with this, let that go — is permissible and does not break anything.
What breaks it is the other kind. The moment it turns into did I do that right, I hope I do it well this time, was that any good — you have stopped directing and started grading. And his verdict on that is blunt: as soon as your intellect gets in the way, game over.
He also names the reason people do it. The habit of analysing everything, he says, comes from not wanting to make a mistake. Which makes it one more thing running on fear.
So today: you may steer. You may not mark your own work.