The NASDAQ stock market rocketed towards heaven for several years. Its decline has been equally spectacular. Four trillion dollars of value have been wiped out in a year. It’s matched its worst fall ever in percentage terms, but it’s done it in half the time. Should we be surprised? No. The statistical concept of “regression to the mean” is working like it always works. Things do tend to even out. What goes up must come down. If it sounds too good to be true, it usually is.