When you follow the trends the odds are in your favor.  For example, if you go long in an uptrend and there is a short term reversal you have various options of extricating yourself from the position.   If the long term and mid term are intact you may even choose to ride it out for a few days.  The same goes for being short in a downtrend.

When you fight the trend your odds of success are correspondingly lower, and you have to be right more often.