By A Long Shot Meaning

(idiomatic, usually with a negative) By a wide margin; indicates a very big difference or disparity.

Example:   He couldn't keep up with me, not by a long shot.‎
  He speaks better than he writes, by a long shot.‎
1883, Mark Twain, Life on the Mississippi,
  'Yes, I do recognize it now. It is the most wonderful thing I ever heard of; by a long shot the most wonderful--and unexpected.'
1913, Jack London, The Valley of the Moon,
  Well, he won't find Billy Roberts a sissy by a long shot.
1920, Sinclair Lewis, Main Street,
  See here: You KNOW you feel superior to folks. You're not as bad as I say, but you're not as good as you say--not by a long shot! What's the reason you're so superior?