Tversky and Kahneman

[Carnite]

The idea here is however one of mathematics, it's called statistical regression to the mean. If you observe the short term changes of someone at the extreme end of the performance spectrum, either end, they're most likely to be seen going in the direction of the mean, i.e. good performers getting worse, bad performers getting better. The idea here is that it takes some fairly extreme circumstances to get them to the peak and thus are likely to drop off regardless of what you do.