I used to fear a lot,whenever I am in darkness in my childhood. But when I realized that the darkness is nothing but the absence of photons in visible wavelength ( from 400-700 nano meters), there is no need to fear. Even we have studied about Light, Heat in our schools but not about darkness or cold, because darkness is the absence of light and cold is due to lower levels of temperature (heat). In the same way negative thinking comes into our mind sometimes, due to absence of positive thoughts. There is a saying that A negative mind can't give you a positive life. Because as the great humans like Dr.Abdul Kalam and Swami Vivekananda said that To change our future, we have to change our habits & to change our habits, we have to change our thoughts. Finally we can say that " The type of tree that has to grow, depends on the seed which you sow".