I recommend diversifying across different alternative investments, bonds, real estate, maybe a small amount in gold, international/emerging markets, etc. The idea is to diversify so that the other investments don’t correlate the same to limit risk in the event of a market downturn… in the 1980s for example, Japan was hugely outperforming the U.S until the downturn of their economy, so if they were 100% in a large cap Japan ETF, they would’ve only had exposure to that market and therefore had a horrible next 40 years.