When bitcoin drops to $30000, this is a disaster for most traders who buy bitcoin and altcoins at a price high. We didn't expect bitcoin to fall this low, so causing altcoins prices to be dumped very deeply. For traders who have already lost over 25% in trading, then it is best not to cut losses because it will make lose some capital. So believe me, the bitcoin price will back up again and altcoins price will rise again.
If you are an actual trader then you got features to save yourself from such crashes like stop loss so you can leave the market with small loss instead of losing half of your capital. And if you missed to exit in that way then you have two choices, whether you can hold until the price increases or accept your loss and start focusing on making the profits with current market movements.