David Powlison answers question 6 of the 15-part Q&A on lusts of the flesh:
6. Does each person have one "root sin"?
6. Does each person have one "root sin"?
With good reason, the Bible usually refers to the "lusts" (plural) of the flesh. The human heart can generate a lust tailored to any situation. Again John Calvin powerfully described how cravings "boil up" within us, how the mind of man is a "factory of idols" [Calvin, Institutes, ed. Battles, 65, 108]. We are infested with lusts. Listen closely to any person given to complaining, and you will observe the creativity of our cravings. Certainly one particular craving may so frequently appear that it seems to be a "root sin": love of mammon, fear of man and craving for approval, love of preeminence or control, desire for pleasure, and so forth, can dictate much of life. But all people have all the typical cravings.
Realizing the diversity in human lusts gives great flexibility and penetration to counseling. For example, one lust can generate very diverse sins, as 1 Timothy 6:10 states: "The love of money is a root of all sorts of evil." Every one of the Ten Commandments--and more--can be broken by someone who loves and serves money. The craving for money and material possessions is an organizing theme for symptomatic sins as diverse as anxiety, theft, compulsive shopping, murder, jealousy, marital discord, a sense of inferiority or of superiority compared to others, sexual immorality that trades sex for material advantage, and so forth.
On the flip side, a single behavioral sin can emerge from very different lusts. For example, sexual immorality might occur for many different reasons: erotic pleasure, financial advantage, revenge on a spouse or parent, fear of saying no to an authority, pursuit of approval, enjoyment of power over another's sexual response, the quest for social status or career advancement, pity for someone and playing the savior, fear of losing a potential marriage partner, escape from boredom, peer pressure, and so forth. Wise biblical counselors dig for specifics. They don't assume all people have the same characteristic flesh, or that a person always does a certain thing for the same reasons. The flesh is creative in iniquity.