Not entirely, since the environment where a particular Wiggin grew up, is affected by his parents' genes.

Well, yes. I was simplifying for clarity.

This makes a lot of assumptions about psychology that are not at all obvious. For example, it might be that if Wiggins have less opportunity to steal ketchup, fewer of them will do it and eventually the strength of the expectation itself will decrease.

The entire point of the example is that the assumption that they want to steal ketchup is what causes it. If you assume they will try (as evidenced by hiding the ketchup when you see them,) then they will conform to expectations by trying. It's a self-fulfilling prophecy of the purest sort.

To be honest, I just made this one up to have a third example, and also to show the level of self-reference possible. It's much less grounded in reality.