Both of these two come to you with a built-in diversification which is amazing and it is to a huge benefit to you and every other investor.
Both an EFT and a mutual fund could include hundreds and sometimes even thousands of individual stocks or bonds in one single place.
This means that if 1 or 2 stocks in that EFT or mutual fund are doing very poorly, it wont affect you that much because there is a chance that other stocks are doing better.
This fact can help you reduce the risk which you are taking on you every time you are making an investment. This can as well reduce your overall losses.