IDIOMS

school of hard knocks

(idiomatic, chiefly US) The source of an education consisting of real-world experiences, especially adverse experiences.

Example: 1870, The Men Who Advertise: An Account of Successful Advertisers, New York: Rowell, p 161:
  Trained, however, in the school of hard knocks, he now had learned the theory of success, and from that time on has had it.
2000, Walter A. McDougall, "Who Were We in Vietnam?," New York Times, 26 Apr. (retrieved 3 Aug. 2008):
  Did Vietnam's school of hard knocks teach Americans to do peacemaking and state building right?