Believe me, there's lots that can be done without special resolutions that could make it difficult or impossible to realise any value.
The main thing to keep in mind is that the shares are normally not tradeable. If you decide you want to realise your investment at any stage, you could well find it impossible to sell to anyone.
Even with a good shareholders agreement, you can find yourself in situations where the shares are effectively worthless.
As an excercise, try asking a bank to take them as security for a loan, and see what value they place on them.