When still a baby, the elephant is tethered by a very thick rope to a stake firmly hammered into the ground. The elephant tries several times to get free, but it lacks the strength to do so.
After a year, the stake and the rope are still strong enough to keep a small elephant tethered, although it continues to try, unsuccessfully, to get free. At this point, the animal realises that the rope will always be too strong and so it gives up.
When it reaches adulthood, the elephant can still remember how, for a long time, it had wasted its energies trying to escape captivity. At this stage, the trainer can tether the elephant with a slender thread tied to a broom handle, and the elephant will make no attempt to escape to freedom.