OnthemorningofSeptember11,2001,PaulMcCartneywasinNewYorkCityonanairportrunwaywaitingtoflytoBritain.Asheabsorbedthenewsoftheunfoldingtragedy,hewondered,“WhatcanIdo?”Theanswer,ofcourse,layinmusic. 　　McCartneyreachedouttomasterdocumentarianandlong-timefriendAlbertMaysles,invitingMayslestodocumenthispersonalexperienceson1...