I never trust people who say 0% risk or 100% of success when they talk about trading or investing.
Everyone who deals with financial markets knows that there is always certain risk and what is the scariest thing is that the plummet usually happens when nobody anticipates it. Speaking about sp 500, I do agree that it is one of the safest assets on the stock market, but there are still risks. It felt very well in 2008, but then it fell sharply and lots of people lost huge amount of money. There is no warranty that it will not happen this week, especially when we cover such environment which can be altered by the single event. Remember 2008, when everything went to the dogs when AIG claimed bankrupt. This caused the overall chain reaction. So, in spite of your current success never forget about hedging your risks and risk management.