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general::
Phrase(s): Give someone an inch and he’ll take a mile. [and] Give someone an inch and he’ll take a yard.
Prov. Be generous to someone and the person will demand even more. (Describes someone who will take advantage of you if you are even a little kind to him or her.) • If you let Mark borrow your tools for this weekend, he’ll wind up keeping them for years. Give him an inch and he’ll take a mile.
McGrawhill's American Idioms And Phrasal Verbs