For the record, no one can predict the future of index funds either. If one's rationale for not investing in Apple is solely based on the fact that it has already seen 25,000% growth, then logically one should not use history as an indicator for future success across any securities. The only thing that makes the index marginally safer is the high amount of exposure and diversification one usually gets, of course.
Using past performance as an indicator to buy a specific company, is idiotic, and isn't even in the same league as using past performance as an indicator to buy the entire market. And not because of risk either. When someone buys the whole market, they are doing so with the expectation that the entire world economy as a whole will continue to grow, because of things like population and productivity (technology makes us more productive) increases. This is the equivalent of looking in a petri dish and watching bacteria grow. We can measure the growth rate, and be reasonably sure it will continue to grow at around the same pace.
Most people are missing a very important aspect of the market...
They don't see that it's a competition. Tell someone they can beat Michael Jordan in a game of basketball, and they will laugh in your face...but give them a sales pitch for "one weird trick" to beat the market, and they will line up to give you money.
When someone buys individual stocks, or an active fund, there is a
competition factor which is missing from the above petri dish example. You're competing against all other market participants, and unlike the bacteria, they adapt and make changes based on available information. When someone claims they can beat that market over the long term, they're saying they can beat over half of all money invested in the market this year, then again next year, and again the year after that...for as long as they live. All by using published, widely known information, that the other market participants (the people they claim to be beating) are aware of. This is essentially the claim:
"<Insert Strategy Here> beat over half of all invested dollars in the past. While this information is public, I do not expect the losers to adopt my published strategy, or change to a better strategy, so I expect it to continue beating over half of all invested dollars in the future."
This isn't just someone saying, "I can beat Lebron James in a 1 on 1 basketball game, you can too!"
It's, "I can beat Lebron James in a 1 on 1 basketball game, every single year, and he knows exactly what I'm going to do each time, and he doesn't copy my strategy or figure out a way to beat me, so I expect I will continue beating him in the future, you can too!"
Compared to:
"Indexing beat or matched half of all invested dollars in the past, I do not expect mathematical laws to change, so I expect it to beat or match half of all invested dollars in the future."
Which one of these statements are you willing to bet your life savings on?