When you elect not to decide, you’re still making a decision. Which is usually the wrong decision. Instead of letting down one party, you're letting down both.
When you are the person that is left to decide, you will make right and wrong decisions. But that’s the not point, what’s important is that you were the one entrusted to make a decision. Being in that position will either bring great satisfaction or sorrow. Either of those emotions is better than being ignored.
People are drawn to decisive people. Even if you make some wrong decisions along the way, make decisions confidently. With time and experience, your ability to decide will improve.