When taming a baby elephant, its trainer will chain one of its legs to a post. When the elephant tries to run away, the chain and the post are strong enough to keep it in place. But when the elephant grows up, it is strong enough to break the chain or uproot the post. Yet the owner can still secure the elephant with the same chain and post, because the elephant has been conditioned to believe it cannot break free. It feels the tug of the chain and gives up — a kind of learned helplessness. The elephant acts as if it thinks the chain's limiting power is intrinsic to nature rather than dependent on a causal factor that held for years but holds no longer.

This is such an excellent allegory that I do need to ask whether there's a citation. I googled briefly and only found motivational texts and discussions of the morality of chaining elephants in circuses.