Sad Sack Meaning

Example : 2007 June 3, Cara Buckley and William K. Rashbaum, "4 Men Accused of Plot to Blow Up Kennedy Airport Terminals and Fuel Lines," New York Times (retrieved 5 April 2015):  One law enforcement official played down Mr. Defreitas’s ability to carry out an attack, calling him “a sad sack” and “not a Grade A terrorist.”2013 April 27, "Movie capsules: Arthur Newman," Boston Globe (retrieved 5 April 2015):  Weary of his drab life with its nowhere job, failed marriage, boring girlfriend, and estranged teenage son, a middle-aged sad sack fakes his death, changes his identity, and hits the road.2014 March 29, Zach Schonfeld, "Film Review: Jason Schwartzman Is Charmingly Inept in 7 Chinese Brothers," Newsweek (retrieved 5 April 2015):  We meet him as he's on his way out, taking the news with equal parts tantrum and sad-sack acceptance.