Move if there is advantage, stop if there is not.- Sun Tzu
This is one of my favorite quotes from Sun Tzu. To me, it encapsulates his whole philosophy on taking action: don't take a certain action unless it will move you forward.
So many times in life, we take action without thinking about the cost or whether it will lead somewhere. We react emotionally to situations without a second thought.
We argue without thinking through our position. We eat without thinking through our diet. We commit to doing a task or favor without thinking through the consequences. We add a feature to our product without thinking through its usefulness.
It's one thing to do something knowing there is a risk of failure. It's another thing to do something that is just pointless.
Of course, knowing what will move you forward depends on knowing where you want to be, but even if you don't know, just stop and think. A few seconds of thinking is worth whatever cost you're willing to blindly pay.