Also, in the interest of one; in one's own interest; in one's best interest. For one's benefit or advantage, as in It's obviously in their interest to increase profits, or Is this policy in the interest of the townspeople? or I suspect it's in your own best interest to quit now. [Early 1700s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.