When he does so, unwholesome states diminish in him and wholesome states increase. At a later time he does not exert himself in what is painful. Suppose, bhikkhus, an arrowsmith were warming and heating an arrow shaft between two flames, making it straight and workable. When the arrow shaft had been warmed and heated between the two flames and had been made straight and workable, then at a later time he would not again warm and heat the arrow shaft and make it straight and workable. At first it may feel like a chore to retrieve the mind from its excursions and return it to the primary object of attention, but as we practice this we gradually get used to it and it can in fact become a most rewarding habit.
Balance is the key.