SPX could double or triple in 8 years

If middle trend line from 1920 holds, the S&P 500 could double in 8 years, that's 10% compound annual growth.
If the value-based forecast happens, it will be first time that stock market went perfectly sideways for a decade. It's more likely to go up and down, while averaging sideways.
If the past decade trend continues for another 8 years, it will run into the resistance line from year 1929 to year 2000, by then the S&P 500 will reach 10K.