The order books are not "real" its mostly bots who place and remove orders on the fly and they react to the price and to the price on other exchanges. There is

The order books are not "real" its mostly bots who place and remove orders on the fly and they react to the price and to the price on other exchanges. There is no way to know how much the price would drop if someone sells for $1MM. also selling all at once, selling it over a few minutes or selling it over an few hours will drastically change the effect. No one who wants to maximize profit would sell fast if liquidity is low because obviously your average at lower then.