The word "courage" comes from the French word for heart, coeur. In essence, it means, "the state of the heart." When we act from our heart, our coeur, the core of who we are, we find the courage to do what it is we feel led to do.
Courage does not happen in the absence of fear. In fact, paradoxically, courage can only happen in the presence of fear; it is fear that makes it courage. Often we perceive others as having courage because they do things we ourselves would be afraid to do - but it is only courage if they are doing something they are afraid to do. Courage is defined by fear, and fear alone, and fear is a very personal experience. If there is no fear, there is no courage.
When we act out of courage, sometimes it feels good, and we feel strong, knowing we are doing the right thing. We feel brave and supported, even in the presence of the fear beneath our action. But other times, even though we know it is the right thing, we are terrified beyond belief. Those are the times Rumi is referring to above, the times when we have to trust and "just go."
When we know where our heart is leading us, and we follow it, we can never go astray. Our heart is the center of who we are, the seat of our intuition, the core of our being. Some of us are more "in tune" with our heart's call than others, but all of us have experienced that call at one time or another. And when we experience it, following it is the only option that will truly satisfy us. The only one.
What is your heart calling you to do, and are you doing it? Where are you being called to be brave? And if you can't be brave, can you find the courage to "just go"?
Having courage isn't about making rash decisions, but it is about being in alignment with who you are. Your heart knows the difference. Listen to it.