There's a passage in Plato's dialogue Protagoras, from about 319E through 320B or so, where Socrates argues that virtue can't be taught; and as evidence, he points to Pericles—the most successful and accomplished (i.e., "virtuous") politician in Athens at the time—whose sons were widely acknowledged to be worthless. If virtue could be taught, he says, then surely Pericles who was himself so virtuous would have seen to it that his sons learned everything he knew, so they could carry on the family fame into the next generation. But in fact he did nothing of the kind. Therefore virtue must not be teachable.
I assume we are supposed to laugh at this argument, at least a little bit. But part of the humor comes because Socrates's remarks are so believable. We are not so accustomed as Socrates was to the idea that the son of a cobbler will become a cobbler, or that the son of a pilot will become a pilot. But we can all think of men who are great successes, whose sons are failures—or (at the very least) whose sons would be failures if they had to compete with anyone else on a level playing field. Examples like that are all too easy to come by.
Why is this so? There seems to be a natural drive on the part of sons to get away from their fathers, to distance themselves in some way. So if the father is shrewd and self-controlled (for example), there is a powerful pressure on his sons to be the reverse. In another sense, I'm pretty sure that one reason I married Wife was to use her as an obstacle between me and Father, to keep him somehow at bay. [I think I've written about this somewhere, but I can't find the post to link to it.]