The index performance definitely is not y=x type of trend.
Take the oldest Dow jones index for example:
1) from 1929 - 1954, it took almost 25 years to recover the financial crisis top 380
2) from 1966 - 1982, the market just went nowhere but sideways between 800 - 1000 for 16 years
3) from 2000 - 2010, the tech bubble and sub-prime crisis has made the market wild oscillating between 8000 - 14000
What I mean is sometimes in our life we need some luck. This is especially true in investing (speculating). Imagine you are living between 40s - 60s in those period and you have to force sell your stocks for your retirement at the market extremely low. It might happen. nothing is 100%. It is just that probability wise market has a good chance(as for past 100 over years, always) to recover. The question is "how long". Japan, another mega economy, took almost 35 years to recover its 1990 peak 39000 this Feb. and China...no comment
To make a fortune, have to plan first, take a risk, and hope for the best.