Quick sells are the most important part of a day trader. You can be an investor and you will have to wait for days even weeks hell with this bear market for months but in the end you are not going to get anything if the market is declining. If however you are a trader than you can sell when its dropping and rebuy when it dropped enough and even have chance at making profits during the bear market days.

Day traders can react a lot quicker and they have the chance to really get out before its too late, investors do not have that chance and they can't take that risk neither. Day trading is better if you want less losses but investing is better if you want bigger gains.