This slogan is about not humiliating people. An important point for the bodhisattva, or the practitioner of this mind training, is to encourage people on their path. However, you could relate with people in such a way that you progress must faster on the path than they do. There are ways of slowing down other people’s journeys so that you can stay ahead of them. But in this slogan, instead of doing that, you develop the other way around—you come along behind the others.
From "Disciplines of Mind Training" in Training the Mind and Cultivating Loving-Kindness, pages 97 to 98.