More Than One Bargained For Meaning

(idiomatic) An unexpected and, usually, unwanted result of a decision or action.

Example: 1874, Ambrose Bierce, "Fables of Zambri, the Parsee" in Cobwebs From an Empty Skull:
  This was more than he had bargained for, and he squeaked shrilly with the pain.
1919, Upton Sinclair, Jimmie Higgins, ch. 22:
  The sound of guns grew louder. . . . [W]hat if the Germans were to break through and sweep over all calculations? This was a little more than Jimmie Higgins had bargained for when he entered the recruiting-office in Leesville, U.S.A.!
1987 July 27, Cristina Garcia, "Law: Casting A Net at Green River," Time (retrieved 23 May 2015):
  [T]hey found much and more than they had bargained for. Nestled amid the weeds and debris near the bottom of the slope was a human skull.
2015 Jan. 14, "Bull elephant gets too close for comfort in Thai park" (video), New York Times (retrieved 23 May 2015):
  A bull elephant gave tourists in Thailand more than they bargained for on Sunday when it sat on and rubbed itself along their cars.