The answer is yes, it IS that simple. But simple doesn't mean it's easy. The S&P500 has a very long track record, it has survived and come out of a few financial crises. To achieve this, you must cover your eyes, ears, ignore the noise/volatility and CONSISTENTLY DCA into the market. The easiest way to do this is to have an automated system. Rain or shine, market crash or market sky rocketing it doesn't matter, you DCA every month.
“A market downturn doesn't bother us. It is an opportunity to increase our ownership of great companies with great management at good prices.” -Warren Buffett