Talking to headteachers at a conference organised by the National College of School Leadership, Zander explains why we should stop listening to the negative voices in our heads and give ourselves and others an A-grade.
He urges people to think positively and be open to possibilities. He argues that we spend too much time and energy being weighed down by negative thinking and downward spirals.
The secret, he says, is to try to live in possibility, and not to take yourself too seriously.