3 Warren Buffett has said that his children's inheritance will be placed in an S&P 500 index fund upon his death

If it's good enough for him, then it's good enough for you
Here's why the S&P 500 is such a great investment:

There is always a risk when investing, but when you invest in an S&P 500 index fund, your risk is much less than investing in individual stocks as a comparison.
The S&P is comprised of companies that span multiple sectors including tech, consumer discretionary and many more.
When one sector declines, it is offset by the gains of another.