Yours truly used to spout this myth when I worked for broker-dealers, before I became an independent Registered Investment Adviser (yes, regulations dictate adviser be spelled "'er" not "'or"). And in practically the same breath we uttered the caveat, "past performance is no guarantee of future results". That's how we were trained to mislead the public. But can anyone tell me how in the world those two statements fit together?? What if I am looking for guarantees? Are there any left that are worth examining? Of course there are. But here's the key: ethical risk transference.
I added that pesky word "ethical" because the vast majority of risk is transferred to those unwilling to assume it. Taxpayer bailouts of the wealthiest people and companies in the world are a good example. Profits are privatized. Losses are socialized.
Taking on risk should be voluntary. Fortunately, there are entities and individuals still willing to take all market risk off your shoulders.