You certainly would not want everything in the Dow Jones, when a company goes broke its taken out of the index and you've lost.
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That's not true, Dow components don't "go broke".
The 30 blue-chip companies, considered to be the leaders of the economy, are chosen by the editors of the Wall Street Journal, a practice that dates back to its inception in 1896.
There's only been 51 changes in its components since 1896.