Hagakure

According to their nature, there are both people who have quick intelligence, and those who must withdraw and take time to think things over. Looking into this thoroughly, if one thinks selflessly and adheres to the four vows of the Nabeshima samurai, surprising wisdom will occur regardless of the high or low points of one's nature.
People think that they can clear up profound matters if they consider them deeply, but they exercise perverse thoughts and come to no good because they do their reflecting with only self-interest at the center.
It is difficult for a fool's habits to change to selflessness. In confronting a matter, however, if at first you leave it alone, fix the four vows in your heart, exclude self-interest, and make an effort, you will not go far from your mark.