That's it... And the relative volumes can be non-equal. 

Now, for your Voskuil example, does that imply that differences in sales volume on either side of a trade CAN effect price?

denlillaapan

econ

Fama: Bitcoin is Dead (Promarket/Capitalisn't)

I like this analogy!

The apple is pulling on the earth as hard as the earth is pulling on the apple. 

But the apple moves because F = ma and the Earth's mass is relatively much bigger than the apple's. For one-sided acceleration to occur, there must be a difference in mass. 

Selling btc for dollars exerts the same sell pressure on btc as the person selling dollars exerts on dollars. 

But the price of btc goes down only if fewer people want btc and the next offer to sell btc at that level of dollars doesn't have a buyer. For a price change to occur, there must be a difference in buyers.