( Story told by Swami Vivekananda )
In some oil mills in India, bullocks are used that go round and round to grind the oil-seed. There is a yoke on the bullock’s neck. They have a piece of wood protruding from the yoke, and on that is fastened a wisp of straw. The bullock is blindfolded in such a way that it can only look forward, and so it stretches its neck to get at the straw; and in doing so, it pushes the piece of wood out a little further; and it makes another attempt with the same result, and yet another, and so on. It never catches the straw, but goes round and round in the hope of getting it, and in so doing, grinds out the oil.
In the same way you and I who are born slaves to nature, money and wealth, wives and children, are always chasing a wisp of straw, a mere chimera, and are going through an innumerable round of lives without obtaining what we seek.
Source: The Complete Works of Swami Vivekananda/Volume 1/Lectures And Discourses/Steps To Realisation