'Ambush,' in this case, means remembering the harm done to us by others and biding our time for a moment of weakness when we might strike back, seeking the help of the powerful or even resorting to witchcraft, and so on. We should relinquish any thoughts of this kind.From Enlightened Courage, by Dilgo Khyentse Rinpoche. Copyright 1993 by Editions Padmakara (Padmakara Translation Group). Published and distributed by Snow Lion Publications. Used by permission.
This site provides an on-line database of commentaries on the Tibetan Buddhist meditation practices of lojong (Mind Training) and tonglen.