I'm writing an article about the First Amendment and child custody; this led me to contemplate the difference between parents' formal powers over their children, and their actual abilities to control their children (I know, Benjamin will give me many more practical opportunities to contemplate this); and this in turn reminded me of this quote from a very different context, Edmund Burke's Speech on Conciliation with the Colonies:

Despotism itself is obliged to truck and huckster. The Sultan gets such obedience as he can.

Being a new father, I naturally have all sorts of creative plans for educating my boys when they get several years older -- teaching them probability theory, geography, history, and more. But when I hatch these plans, I try to keep in mind the classic military saying:

No battle plan survives contact with the enemy.