It doesn't follow that because he did worse than the optimal strategy his strategy wasn't equally as optimal. It could be that the strategy he followed is as optimal as the other one, but is subject to chance and he got unlucky.
You can't say "strategy A produced a better result than strategy B, therefore strategy A is a better strategy" based on a single example of someone using strategy A.
The real point, for me, is not so much "Trump could have done better by investing in index funds", it's "Trump's business underperformed the market".
And, yes, underperforming the market over 30 years or so isn't proof of anything much; he could just have been unlucky. But for the exact same reasons, the fact that Trump's a billionaire isn't proof of anything much; he could just have been lucky. (He was: he inherited a lot.)
The only point I'm making is this: the fact that Trump is rich is not very good evidence that he's a great deal-mak...
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