Since the 50s, the S&P 500 has historically averaged around that figure. But an average is just that, an average, some years will do better than the average, others worse, sometimes by substantial margins on both enda.
The 50s were the best decade in terms of annual returns on the S&P. As the years pass, performance metrics from these times are no longer informative for current investors - those who invested in those decades are dying or dead. With each passing day, a larger proportion of the current investor class has only the "lost decade" of the 2000s as its only investment decade. There is almost no chance a typical buy and hold investor 35 or younger will see an average 8% year over year return in something vanilla like the S&P. Too many years of poor performance have gone by and there is no cause to believe a real, inflation adjusted boom is in our future.