“Fisher was quite right to highlight the need to think about the future. We must, after all, weigh up our chances and make our decisions. But, as his contemporary John Maynard Keynes famously remarked, sometimes “we simply do not know”. And since Fisher was eventually ruined, while Keynes died a millionaire, a little agnosticism comes in very handy. In any case, we must learn to live with uncertainty. Perhaps we should obsess less about the question, “Will it happen?” and devote more thought to what we would do if it did.”
Source : Why pollsters so often seem to get it wrong | Financial Times