SPY是普标500ETF, 风险大于 VTI是Vanguard Total Stock Index ETF。

We will need to have total stock index fund with 1,000 to 2,000+ stocks in the fund, the risk is more diversified.  Individual stocks are more riskier than sector funds (100 stocks), sector funds are more riskier than S&P 500 Index (500 stocks), S&P 500 Index is more riskier than Total Stock Market Index (1000 to 3000 stocks).