[ThrustVectoring]

You still have some optionality as long as you're still within the vesting period. You can quit, forfeiting the unvested portion of your grant. IIRC you even get refunded a prorated portion of the purchase cost, too.

You may also have or be able to negotiate getting an explicit put option at the same price, too. That is, if you can buy shares at 20 cents a pop, you can also sell back to the company any shares you bought at 20 cents also at 20 cents. (NB: put-call parity proves that the value of "call + cash required to exercise" exactly the same as "underlying security + put at same strike", so you have exactly the same amount of value. Well, so long as the assets don't yield dividends, at which point American options that allow early exercise have the same value as European options that don't, and start-ups generally don't pay dividends.)

[sk5t]

Where do you suppose the money to refund the unvested early exercise, or to satisfy the put option, will come from if the firm goes belly-up? Wouldn't the granting of the put option confer some quantifiable (taxable) financial benefit as well?