Sifrei Mitzvot do Powtórzonego Prawa 21:9

Each and every one of the sons of man has many innate tendencies which differ one from the other and which are extremely afar. There is one man of a feverish temperment, constantly vexed, and there is another man of a calm disposition, without angry moods whatever, and if he does show anger it is but one bit of anger in many years; one man is overmuch supercilious, and another man is extremely unobtrusive; one is sensual, whose being is never stilled by the pursuit of propensity, and one is so pure-hearted that he feels no craving even for the barest necessities of the body; one's being is so greedy that the world's money will not satisfy him, as the subject is spoken of: "He that loveth silver shall not be satisfied with silver" (Ecc. 5.10); and one's being is so restrained that he considers enough even part of the little which is insufficient for his need and he will not pursue to attain all needs; one suffers hunger in his effort of hoarding and does not eat a cent's worth of his own without great torture to himself, and another wastes his money with his own hand deliberately. And of such ways are all the rest of the tendencies, as the optimist and pessimist, miser and philanthropist, cruel and merciful, coward and stout-hearted and the like.

And there are between each and every extreme tendency of an opposite vein mean tendencies one distinct from the other. Pertaining to tendencies in general, there are such tendencies which a man acquires at his birth, in keeping with the nature of his body; and there are particular tendencies to which a particular person is by nature prepared to acquire them more aptly than other tendencies; there are among them such which do not come naturally to a person at his birth, but which he learns from others, or by leaning towards them as a result of a thought invented by his heart, or by having heard that this particular tendency is good for him and proper to follow it, and he did follow it until it was set in his heart.

The two extremes in each and every tendency is not a good way, and it is not proper for a man to follow them, nor to have himself instructed in them. If one finds his nature leaning toward one of them, or susceptible to one of them, or if he already acquired one of them and followed it, he should turn himself toward goodness by following the path of the good which is the straight path.