Donahue (D) had bought some clothes from Mitchelman for $21.55, and Mitchelman came to D's house for payment. D offered $20 for the clothes. D took the $20 and stated that he still wanted $1.55 more. D attacked Mitchelman and choked him, demanding his money back. D continued in his attack until Mitchelman surrendered $29. D honestly believed that $20 was a sufficient price for the clothes and demanded his money back, saying that Mitchelman had no right to ask for additional sums. D was charged with robbery. The judge charged that if D did the act, his honest belief was of no consequence. D was convicted. D appealed.