I can’t believe people smart enough to acquire the wealth for that excursion
You do not need to be smart to acquire wealth.
Of the people in the sub, I am confident that 4/5 of them were born into wealth, and I can't really find any information on the other one.
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The Dawoods (father and son) were only wealthy because their father/grandfather was wealthy.
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Stockton Rush was also born into wealth, his family made their money from oil and shipping.
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Can't find a lot of information about Hamish Harding, but he was flying aeroplanes at 13 and went to a prestigious private school called The King's School, so it's safe to say he was also born into considerable wealth.