Although it doesn't necessarily do away with the entire message, I'm with you in thinking that the premise is a bit of a stretch. My initial guess at a reasona

Although it doesn't necessarily do away with the entire message, I'm with you in thinking that the premise is a bit of a stretch. My initial guess at a reasonable explanation was that we're more inclined to believe we deserve a treat/reward after doing work, and memorising a long number is obviously more 'work' than memorising a short one.