Mujaahidah against the Nafs in its urges for sin is acquired when the nafs is opposed to a certain degree in even its lawful desires, e.g. refusal to fulfill immediately the desire of the nafs for some delicious food, its urge for such food being rebutted and only fulfilled after vehement desire so that the nafs does not become frustrated. When one becomes accustomed to oppose the nafs in things lawful then it will become relatively simple to oppose the sinful urges of the nafs. A person who grants his nafs absolute freedom in the Mubaahaat (lawful things) at times will not be able to suppress the urge for sinning.