You can't take net worth away because it's just an estimate of what someone is worth. It may eventually be possible to turned into dollars and cents without losing too much in the process, but almost universally it can't immediately be exchanged in such a fashion.
Even more so when we're talking shares in a company that is not yet public, e.g. a founder's shares. At that point the valuation is complete speculation, based on what the company may be worth in some hypothetical future IPO. There's no actual price discovery since there's no public trading of such shares.