Why is it said that a one-sided trend cannot be reversed?

Originally, a one-sided market trend theoretically presents a great opportunity for making profits, but people have become accustomed to the ups and downs of the market, and are thus intimidated by what seems like an irrational trend. For example, in a one-sided bull market, one might think that prices have already risen too high and will eventually fall, so it makes sense to short at a relatively high price! From my experience, many people suffer significant losses or even get kicked out of the market by going against the trend without setting stop losses in a one-sided market. Additionally, it is extremely difficult to persuade others to go long in a one-sided trend. Even now, I always emphasize not to go against the trend. Why?

Firstly, we often say, "It is not advisable to go against the trend in trading," but who truly understands this statement? What is a trend? What is a major trend? A one-sided market is the largest of the major trends! Can you find a larger trend? If you go against it, it is more foolish than missing an opportunity! A good opportunity can turn into a disaster! In real life, it is hard to find a vivid metaphor to illustrate such foolishness. If this isn't called going against the trend, what else can be considered as such?!

Secondly, you might think that the upward or downward trend has lost momentum, so it is worth taking a position against the trend, as the saying goes, "a strong bow cannot penetrate a thin cloth." While this statement is theoretically correct, in practice, trying to block a strong bow with thin cloth is likely to fail. It is challenging to determine where the "end" is and at which precise point you should stand. Of course, nothing is absolute; if you indeed see a highly effective historical resistance level, trying to short may not be unreasonable, but you must set a stop loss. In the futures market, having a strict stop loss and disciplined approach is absolutely necessary.