Negatives Are Hard To Understand
The clip above is a funny skit from "Mr. Show," featuring grocery stores competing with advertisements. One says "no rats," implying that the other has them.
A study presented participants with two glasses of water. They watched sugar get poured into both. Then, after that, one glass was labeled `poison' and the other `sucrose.' People were averse to drinking the one labeled poison. Interestingly, a condition in which the glass was labeled `not poison' was also avoided, suggesting that the subconscious does not understand negatives (Rozin, Millman, & Nemeroff, 1986).
I recall once at Georgia Tech there was a water fountain that had a sign on it saying that the water from it was safe to drink. A colleague came into the building and asked me if the water was safe. Interesting that she'd ask when the sign clearly said it was safe. The sign gave her reason to suspect something was amiss.
What am I doing with this? Well, I think that the default value of any proposition encoded in your mind is "true." I think it takes effort to encode a negation, and it takes effort to recall it. I would love to do an experiment that tested this, showing that people under cognitive load would mis-remember false propositions as true.
In real life, Fairsley's "no rats" statement would probably hurt sales at Fairsley's too.
Rozin, P., Millman, L., Nemeroff, C. (1986). Operation of the laws of sympathetic magic in disgust and other domains. Journal of Personality and Social Psychology, 50(4), 703-712.