It is for minimizing the possible losses.
A trader knows how to manage the risk and even calculate it if it's needed. This has become a standard for the traders because they're all for the safety of their trades from huge losses.
You are right, because no matter how good a trader is, he can only guess the direction of the market, he can lose, he can make mistakes. So risk management by using features in trading such as stop loss is absolutely necessary. That is support for the analysis because it is better to lose a little than to lose a lot.