Finally, remember that ETFs move with the market at large — making them subject to all the same volatility. (grow.acorns.com)
When we compare the 8 ETF portfolio to a 50/50 portfolio consisting of 50 % SPY and 50 % AGG, we see that the Permanent 8 portfolio significantly outpaced a 50/50 portfolio since 2008 with about the same volatility: (scottsinvestments.com)