How long does is take for the cultural memory of a "great deception" to fade away, so you can do another one?

Do we factor in Attention Deficit Disorder for our answer? So many are distracted mentally either by handicap, mind altering controls or tainted food diets that disrupt thought processes.

I have a few people around me who haven't paid the slightest amount of attention to any of the deception. That's mind boggling!