Cause either total success or total ruin, as in This assignment will make or break her as a reporter. This rhyming expression, first recorded in Charles Dickens's Barnaby Rudge (1840), has largely replaced the much older (16th-century) alliterative synonym make or mar, at least in America.
American Heritage Idioms
Phrase(s): make or break someone
[of a task, job, career choice] to bring success to or improve, or ruin, someone. • The army will either make or break him. • It’s a tough assignment, and it will either make or break her.
McGrawhill's American Idioms And Phrasal Verbs