burn one's bridges

Also, burn one's boats. Commit oneself to an irreversible course. For example, Denouncing one's boss in a written resignation means one has burned one's bridges, or Turning down one job before you have another amounts to burning your boats. Both versions of this idiom allude to ancient military tactics, when troops would cross a body of water and then burn the bridge or boats they had used both to prevent retreat and to foil a pursuing enemy. [Late 1800s] Also see cross the rubicon.