make or break

adjective

1. either completely successful or utterly disastrous: a make-or-break marketing policy.

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.