I choose the rule that most of us have been warned not to break: don’t divide by zero, because when I heard it the first time I wondered why we can't do it? Why is this rule exists in mathematics? What is so wrong with dividing by zero? So I start asking and searching until I was convinced then I was completely sure that all the students have to know that. I also choose to answer this simple question in order to encourage science lovers to stop accepting math as rules and declarations and to ask and think critically whenever they find something that feels intimidating and strange. We all should believe that: curiosity is the essence of our existence.