"My Teachers are My Hero"

A teacher is a person who always teaches us good things and guides us in the better way. when I was a child, we called our teachers as a "Pahlawan Tanpa Tanda Jasa" (Indonesia language). I didn't understand actually, what is the meaning of that sentence. In the past, I just realized my teachers is a hero because they shared their knowledge to us. Moved to the junior high school I am still wondering about that sentence. I saw they didn't do anything to prove me that they deserve called as a hero. They just teach the same things similar to when I was in elementary school.