If you had invested EVERYTHING into the S&P 500, based on Dow Theory analysis and reinvested all of the dividends, you would be sitting on a 21.99% annualized return.
For long term investors, this is spectacular. Most long term investors want an average return of 10%. 12% is considered excellent over the long term. So consider that next year or the year after will see some movement into a bear market (maybe!). When that comes, we will either want to average down as the market bottoms, or we will want to have the guts to cash out proactively, ride the wave down and re-invest when the indexes confirm a reversal in trend.