Trading and investing are not one-dimensional disciplines.
People very often make the terrible mistake of stagnating on one main idea, not allowing themselves to be flexible enough to change or to have a Plan B in case the primary scenario becomes invalid.
Every setup can be invalidated; it's a matter of probability, which can change in an instant due to additional charts.
The main goal of a trader/investor is not to be right 100% of the time but to have a good track record in the long run, which means that good trades should outweigh the bad ones.
In this context, using stop-losses and closing trades below SL is crucial, and personally, I prefer to lose a small % and move on rather than painfully holding a potential -30% because... "just another -3% and I'm sure it will bounce back."
For "long-term investments," the story is very similar, and that's why you should look at the charts because if an asset loses key levels, it will fall significantly (or not, depending on the importance of the level below).
Stop holding blindly, which is why 90% of people lose money in this space.
A failed trade should not affect your overall path, especially from a psychological standpoint.
Things happen in life; the key is to learn from this mistake and improve the next time.
Those who are stuck in the past will never achieve great success in the future.