Stock can't go negative.If you own stocks in (say) game spot and they dip to being worth minus 10 million dollars does that effect your actual balance or is it all notional until you choose to sell it?
Does it just mean that you lose what you initially invested? (Because the stocks aren't worth shit.)
By buying and selling shares you can only lose your investment. If you buy and (particularly) sell options you can lose many times your original investment cos you arr promising to sell someone shares at a particular price which might be much lower than the price that it is trading... the result being that you have to buy them at the high price just to keep your deal. And as there is no limit to how high it climbs your potential loss is unlimited.