Psychology works simply: when the market falls, it seems it will fall forever; when it grows, it seems it will grow endlessly. A person sees a growing portfolio but cannot sell because they want more. As a result, profits are not secured, and when the correction begins, everything disappears.
That is exactly why there must be a pre-developed plan. Sell orders must be placed in advance, in specific zones where profits are secured automatically — without emotions. If in the long term you manage to take about 70% of the major market movement, that is already a perfect investment strategy. Those who understand cycles and discipline do not lose their heads.