If I could not fail:
The cure to the main reason of death: age. Life is a pain when you always have to worry about age. With age comes sicknesses, weakness, and death. There is too much in life to explore and too little time to accomplish anything. For about a third of our life was spent on education and development, another third is spent sleeping. We only have 1/3 to actually work and play. That is not enough. If I could not fail, I would try to create something that completely gets rid of aging. What if you are allowed to live the best moments of your life forever? Even if it gets worse, there are more things to not worry about. To conserve the resources on this planet, this substance is only administered to the people that earned it.