Financial mathematics has something cruel about it. When studying it, it is not difficult to see that it works, that is, that the long term really does confirm the theory of multiplication. Although recent, it already has sufficient historical data to estimate with some certainty the results of different scenarios, including those that are unforeseen. Risk, too, can now be quantified in fairly reliable figures. But all of these calculations, all of these estimates, all of this sufficiently safe way of operating, with more than satisfactory results, is always based on percentages. No matter how sophisticated the calculation or how powerful the computer, it is impossible to escape this constraint: a percentage is always relative to the principal.