I agree that "infinite riskless investments don't work" and agree with the "possibility of consistent good rate of return." Many investments are indeed finite on a human scale. An investor will almost always want their money back with some return, no? At some point they'll take their money out of the investment or market and spend it. The particular issue was the claim that the Medallion Fund from Renaissance Technologies was a good example for a consistent rate of return. They may have done that but how would we know? Their data is self reported, and as far as I'm aware there's no publically available audits of their performance. Even if there were, we have evidence of their cheating at taxes through abuse of options. If I were you, I would take their claims with a very large lump of salt. Do you know who else claimed guaranteed double digit rates of return? Bernie Madoff. We might not have found out about his fraud either if it weren't for some whistleblowing and for his admission of wrongdoing.

The Medallion Fund may have returned 30-70% over decades. Do we really know for sure? I think you'd have been better off simply suggesting index funds for consistent returns for the average person or citing Warren Buffett or Bill Gross for generating alpha/consistent returns.