I think what you are referring to is why do we need to make a topic then proposing it to research teacher. It is because, first of all, you need to know if the topic that you will propose is effective, economically and environmentally safe and of course the availability and cost or expenses of the research project. It must be approved by the research teacher before you conduct a research about it. So generally, we need to know how to make a proposal of topic to know if your research project is significant to the society or it can add up to science.