leave to someone's own devices
Allow someone to do as he or she wishes. For example, Left to his own devices, he would hire someone to do the yard work. This expression, uses device in the sense of “a plan or scheme.” [Late 1800s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.