be the making of

Be the means or cause of progress or success, as in Marriage will be the making of him. This idiom, using making in the sense of “advancement,” was first recorded about 1470.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.