But what really happens around a freaky Friday? All options expire, so large investors (typically large mutual funds or hedge funds) need to rebablance their portfolios all at the same time according to their pre-defined hedging strategy. So all the funds buy the S&P500 underlying at the same time just before Triple Witching. Just after the triple Witching the fund's artificial demand vanishes which very often leads to a little decline in the stock prices of the S&P500 constituents. So you need very strong positive news to balance this effect and push up the markets on the week after triple witching.
You would be a fool to ignore it.