Terrorists are predisposed to attribute success to their technique whenever plausible (62–64). Pape claims that "recent suicide terrorist campaigns ... are associated with gains for the terrorists' political causes about half the time" (64–65). Hamas's success is difficult to evaluate, but Hamas spokespersons express belief in their own success (65–73). Terrorists learn from each other; the spread of the method is therefore neither irrational nor surprising (73–75). But suicide terrorism has failed "to compel target democracies to abandon goals central to national wealth or security" (75–76).