The difficulty with compound growth is that nothing much appears to happen for a long time, and then a great deal happens quickly. A sum growing at seven percent a year roughly doubles in a decade, which sounds modest. Over four decades it doubles four times, ending sixteen times larger. The first decade produces the smallest gain in absolute terms and requires exactly the same patience as the last. This is why saving started early is worth so much more than the same amount saved later, and why the advice is so often given and so rarely followed.