One of the classic lines from DOUBLE INDEMNITY:
Edward G. Robinson as Barton Keyes to Fred MacMurray ( Walter Neff):
“I picked you for the job, not because I think you’re so darn smart, but because I thought you were a shade less dumb than the rest of the outfit.
Guess I was wrong. You’re not smarter, Walter, you’re just a little taller.”
You can hear Edward G. Robinson’s resigned tone.Neff has been like a son to him, he mentored Neff, he expected him to go far in the insurance business. Instead he finds that Neff is a killer.
Edward G. Robinson
Fred MacMurray
And the blonde who set the drama in motion.
Barbara Stanwyck, Fred MacMurray
Vienna's Classic Hollywood 
The layering and depth of the relationships between the characters is one of the great joys of this movie, isn’t it?
Yes, the skilled writing is everything. “You’re just a little taller” is a killer line.