Only if you look at American stock market data. And that's extreme cherry-picking, because the American stock market is by far the best performing over the last century. What are the chances the American stock market will be the best performing next century?
The standard claim is that "even if you bought at the absolute worst time, if you held for 10 years you would have been positive after inflation". This statement is true for the US stock market, but not true for many other stock markets.
There's "lost decade" periods in the US market as well, that's why you shouldn't invest in a single market, and should apply unit cost averaging instead of dumping all your money at once.
Only if you look at American stock market data. And that's extreme cherry-picking, because the American stock market is by far the best performing over the last century. What are the chances the American stock market will be the best performing next century?