When do people need to react? Many people in their lives will run across situations that require them to make the decision to fight or flee. Do you really know which is best? These could be very complex and difficult long-term problems. Problems such as unemployment, underemployment, health issues, love battles, family squabbles or the like. I guess the only real way to tell what the good option is, is to determine what you are trying to win. If the objective isn't worth fighting for then it is time to leave the situation. But sometimes the objective is worth fighting for. Perhaps your own personal freedom is worth fighting for... Maybe you have been in a life-threatening situation which requires you to fight a stronger enemy than yourself.
Some might say, it's better to fight and have dignity, but this isn't always true. If you know certain death is upon you perhaps its better to pull back and fight the longterm battle. By doing many good small things you might be able to combat the opponent in your life indirectly. Sometimes there are no good options, fight, run, hide... Whatever you do, just realize that the universe runs on effort. Decisions made on fear alone are usually bad. You have to analyze your longterm objectives and think through what you can do to make them a reality.
Don't get caught up in the small stuff, remember that the evolution of your soul is always the most important thing, secondarily to that you can look at fighting evil as an important quest. Frankly, the latter is something not many people pay much mind to, but fighting in a way that makes sense, legally, emotionally, spiritually etc. is important. We all have weapons to fight against injustice and immorality. Many times they are things like kindness compassion and hard work. They might not seem like much, but they are more powerful than you might think.