I totally understand the point you're trying to make, but also...if your friend put their $40M in an S&P500 index 20 years ago, it'd be worth $238M today. So more like 6x rather than 10x, but still, not bad.
The people I know personally with that level of wealth will typically set up family trusts to do that and manage how the wealth is distributed to the family, generally some stipend for living expenses + covering education and healthcare costs. The original people setting up the trust give up direct access to that portion of the money for the benefit of their heirs and beneficiaries. i.e. it's no longer "their" money in the personal sense.