Jamieson, Fausset and Brown on Jeremiah 17:9

9. deceitful--from a root, "supplanting," "tripping up insidiously by the heel," from which Jacob (Ho 12:3) took his name. In speaking of the Jews' deceit of heart, he appropriately uses a term alluding to their forefather, whose deceit, but not whose faith, they followed. His "supplanting" was in order to obtain Jehovah's blessing. They plant Jehovah for "trust in man" (Jr 17:5), and then think to deceive God, as if it could escape His notice, that it is in man, not in Him, they trust.

desperately wicked--"incurable" [Horsley], (Mi 1:9). Trust in one's own heart is as foolish as in our fellow man (Pr 28:26).