> What technically prevents them to run away with all stocks? It's called the law. > Well, it would be stupid to trust the broker. [..] I currently manage it

> What technically prevents them to run away with all stocks? It's called the law. > Well, it would be stupid to trust the broker. [..] I currently manage it by simply having accounts with several[...] If you believe it's "stupid" to trust brokers, spreading your exposure across several of them may protect against a complete loss. But it also increases the risk of some loss and, on balance, has exactly the same expected value. The law diminishing marginal utility may put your strategy slightly ahead, but the difference is similarly marginal.