Your spirit must constantly assert itself because your body is constantly exerting itself. As soon as you stop working at your spirit, then your body will have complete power over you.
What is not clear should be cleared up. What is not easy to do, should be done with great persistence.
We suffer from our vices, and try to struggle with them, and the reason for this struggle is that we are not perfect. But our salvation is in this struggle with vices, and if God were to take away our ability to fight our vices, then we would be left with them forever.
— Blaise Pascal
A good thing is always done with an effort, and when the effort is repeated several times, then a good thing becomes a habit.