Water as such or fire as such cannot move a train; they must both cooperate to produce the third thing, steam. The steam moves the engine forward. The curbing of the mind, it is, that takes you to the winning post. Petrol and air must both unite to form the mixture of gas, which ignites and produces energy to haul a car.
(From : Sai Veda, The Word of God, sayings of Bhagavan Sri Sathya Sai Baba)