Since January of 1986, the research firm DALBAR has been compiling data measuring how the average investor performs over time. The results are pretty harrowing, and they might surprise you.
I guess I didn't explicitly point out that I was referring to people that invest regularly in a low cost and efficient manner and don't bother trying to time anything. It's well known how poorly the average shmuck does compared to benchmarks of what they should be able to get. If people make bad investment decisions, no real guess at returns over time will be useful to them. But since I KISS for the most part I do find it useful and highlighting the math of compounding is a worthwhile exercise when seeing what savings rates can yield what return decades in the future.
I mean the post I replied to suggest saving $300K a year for 22 years would yield $7M. That's just nuts. You could invest in TIPS or 30 year treasuries and do better than that.