A well considered investment into the securities of a good company is beyond dispute. That good money managers exist and can deliver above market returns is also persuasive. That well-run companies with rising cashflows boost their share prices is a fact. The problems with this gross oversimplification are obvious. Economies exist primarily to distribute wealth.
Financial markets price the cashflows of companies and securities.
Sometimes even developed financial markets are gripped with the same valuation disability that recently possessed the citizens of Albania and Romania. It is impossible to pick the peak of the market until well after the fact. When markets depart from reality there is generally widespread agreement on what seems to be persuasive rationale. You underperform, so put your money in an index fund, and etc. These slogans have some basis, but are dangerous in their oversimplified form.