The reason is that trends can be left for long periods. So if you are trading against the trend, you can come out many times. But if you are trading in the direction of this development, you may find yourself making some great gains
You do not even have your timing absolutely spot in many cases, either because the trend will often come to your rescue. For example, if you enter a trade in a rising trend in the market and prices fall, you may well find that at some point the trend will prevail and your long position will eventually pass into profit