Trends are divided into downward trends and upward trends.
Under the trend, short positions are in principle;
On the trend, in principle, the position is full.
The bottom structure on the trend is meaningless, because there is nothing to buy with a full position; the top structure under the trend is also meaningless, because there is nothing to sell with a short position. If there is a bottom structure under the trend or a top structure on the trend, up to 40% of the position can be bought or sold.
In other words, keep at least 60% of the position when the trend is trending, and buy up to 40% of the position when the trend is trending.