A recent Fidelity artice dropped what was to me twin bombshells: That the value of dollar-cost averaging and of time diversification are both myths or "optical illusions":

"Meir Statman, a finance professor at Santa Clara University and author of "What Investors Really Want," had these pearls of wisdom about dollar-cost-averaging and time diversification. "They are both based on the equivalent of optical illusions, but they are useful optical illusions," he said. "After all, movies are optical illusions as well, yet we don't complain. We don't even complain when movies lie, telling us fiction."

According to Statman, dollar-cost averaging is commonly recommended as lowering risk. "This is false," Statman said. "But it does lower regret. People who are afraid to invest $100,000 into stocks in a lump sum because the market is sure to drop the day after, can do it at $5,000 each month for 20 months. This also works for people who are afraid to cash $100,000 of stocks in a lump sum, fearing that the market would zoom as soon as they sold."

As for time diversification, it's the claim that the risk of stocks is lower when time horizon is longer. "This is false as well, said Statman. "But time diversification can be a way to soothe fears of investors who hesitate to invest in stocks," he said."

https://news.fidelity.com/news/article.jhtml?guid=/FidelityF...

Note that there is no explanation, just this professor's flat statement that both are false. Is it just one air-headed professor's view, or is is this really the case? Do the contributors here agree?

Thanks,

Case