Why do people sin naturally according to Ephesians 2:3?

Les teaches from Ephesians 2:1–3 that the people Paul describes were dead in trespasses and sins, meaning without spiritual life, not physically dead, since they were still walking in the flesh. In times past they walked according to the course of this world and the prince of the power of the air, the spirit working in the children of disobedience. Les identifies these as children of Adam, who disobeyed by virtue of Adam’s disobedience. Verse 3 says all had their manner of living in the desires of the flesh and mind and were by nature, naturally. Les illustrates this with even sweet two-year-olds: they sin just as soon as they can, because they are children of Adam. He says humanity are practitioners of the things of this world, desiring the lusts and pleasures of life because it comes naturally, like the old song “Doing what comes naturally,” giving in to natural inclinations.