This baffles or puzzles me, as in I don't know how he does it—beats me! This term originally may have alluded to a winning poker hand. It may also be related to the even earlier usage of beat for “astonished” or “at a loss.” [Slang; mid-1800s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.