The profit taking between traders and investors is different, but in principle it must have the price target. Before we buy/sell in the market, we must have a careful plan so that we can stay in the market for a long time.
The market is very dynamic. No one in this world can accurately predict the direction of the market. If you are absolutely sure of the prospects of the portfolio you hold, then I don’t recommend selling everything. If you are not sure, it is best to take all profits and mix in a new portfolio that is still promising. The market will always go through a "bearish-sideways-bullish" cycle, so we need to learn to take profit/stop loss.
Your right the market signal is very volitale and hard to predict. For traders they always look at the movement of the candle stick specially on those doing day trading method. While the investors mostly engage in long term investment which also expert on there thing. They both have one target and that to gain profit. That stop loss you talking applied by the traders as they opposite from investor, traders doing short term investment mostly