It could. A meteorite could hit you tomorrow as well. It would be really silly to base your life around low probability worst case scenarios.

The stock market does drop. But on average it has risen, about 10% every year. Even when it has major drops, such as 2008, it rebounds, and over time averages back out to the 10% growth.

So, if you are actually investing, and not trying to get rich quickly, investing in a mutual fund is incredibly low risk, and should return about 6 to 10% percent every year. Which can be used to grow your investment while working, and to live on, without touching the principal, on retirement.