Why do they pick up on the "bad" examples to follow?

We were eating dinner last night and it was noisy.  Of course it was noisy, it's always SUPER noisy at dinner at our house no matter what we do.  Everyone has much to say about their day and they all try to talk at once.  And there's always someone complaining/ whining very loudly about which part of the meal they don't like.  So anyway, it was noisy.  Caleb smacks is hand down on the high chair and yells, "SOP-IT, SOP-IT!" (i.e. stop it).  I have noooo idea where he got that from.  (hehe).  It worked to calm the noise this time because everyone stopped being loud long enough to laugh at him!