-- St. Tikhon of Zadonsk (d. 1783), Journey to Heaven: Counsels On the Particular Duties of Every Christian, pp. 141-142
One year later...
We note five causes of sin:
1. The corruption of human nature. Man is conceived in iniquity and born in sins, as the Psalmist says, 'For behold, I was conceived in iniquities, and in sins did my mother bear me' (Ps. 50:7). The sinful passions with which he is born incline and draw him to sin. 'O wretched man that I am! Who shall deliver me from the body of this death?' (Rom. 7:24). Corruption and accursedness have entered into man from the fall of Adam. This inclines a man to every sin. 'That which is born of the flesh is flesh' (Jn. 3:6). But Christians must stand against inclinations and passions and struggle according to the power of holy Baptism and the vows made then, and not allow them to progress into deed.
2. The devil leads man to sin. Of this the Apostle says, exhorting Christians to be on guard against him, 'Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour. Oppose him firm with faith' (I Pet. 5:8-9). The Apostle says the same in another place, 'Be strong, in the Lord, and in the power of His might. Put on the whole armour of God, that ye be able to stand against the wiles of the devil. For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of darkness of this world, against spiritual wickedness in high places' (Eph. 6:10-12). These unseen enemies are always eager for our destruction, O Christian! Be vigilant, and make haste to guard against every sin. We must not, therefore, slumber.
3. The seductions of the world also lead toward sin. We see that evil grows; one does such and such a thing. Another either sees it or hears of it, and recklessly imitates it. Temptation is like a pestilence that begins in one man and infects many living near him. 'Woe unto the world because of offences! For it must needs be that offences come; but woe to that man by whom the offence cometh!' (Mt. 18:7).
4. A cause of sin is often the bad upbringing of children. Such children, when they come of age hasten toward every manner of evil. This comes about from the carelessness of parents. Give heed to this, fathers and mothers!
5. Habit strongly attracts a man toward sin. We see this evil; we see that drunkards are always drawn toward drunkenness, thieves toward theft, fornicators and adulterers toward impurity, slanderers toward slander, and so on. For their habit draws them like a leash toward sin, and they are drawn toward the sin to which they have become accustomed just as a hungry man is drawn toward bread and a thirsty man toward water.
-- St. Tikhon of Zadonsk (d. 1783), Journey to Heaven: Counsels On the Particular Duties of Every Christian, pp. 67-69