30 years good enough for you
And Mr Buffet's investment company has beaten wall street for decades.
You are believing all that advertising the index fund managers are putting out and your bank is aggressively selling you.
The difference is that he has significant inside information into many of his investments. He deeply researches the companies involved, talks to their owners, etc. He is far smarter than your average investor but he also purchases companies with far more information than your average investor.
If you go to buy a private company you can get a lot of non public information. The same thing happens when you try and take a public company private with the caveat that you can only use that information to back out of a deal not make your first offer. AKA, you get to do an audit after the terms where agreed upon and only get to back out of you discover major issues.
And Tesco didn't work out to well for him anyone who follows the markets could have told you that the supermarket where doing lots of dodgy stuff
Buffett himself says that you the average joe should invest in an index fund.
Berkshire hasn't really done very well since 2000. He's kind of coasting on past reputation at this point.
Index funds are usfull for some investors for some of their investments but they are not the holy grail.