Index funds just reflect the entire market. The stock market crashes frequently, e.g. 2001, 2008, etc. In a bad crash, you could lose 50+%. And there's no guara

Index funds just reflect the entire market. The stock market crashes frequently, e.g. 2001, 2008, etc. In a bad crash, you could lose 50+%. And there's no guarantee of a swift recovery: in Japan, levels have still not recovered to the pre-1991 highs. With bonds however, if you are buying a high credit quality bond, you will almost certainly get your money back at maturity (in the interim, the price can decline due to changes in interest rates). With a long enough investment horizon however, being invested in the entire US stock market has historically worked out very well, and should hopefully continue to do so in the future barring very extreme destabilizing world events. You should get growth that you cannot achieve with bonds. So it all depends on your time horizon (e.g. longer than an economic cycle) and risk appetite (appreciation vs. maintaining principal).