Sin begins in the heart, inwardly, then manifests itself out.
Sin is contagious.

Hosea 4:8

They eat up the sin of My people;
They set their heart on their iniquity.

Psalms 1:1-6

Blessed is the man
Who walks not in the counsel of the ungodly,
Nor stands in the path of sinners,
Nor sits in the seat of the scornful;
2 But his delight is in the law of the Lord,
And in His law he meditates day and night.
3 He shall be like a tree
Planted by the rivers of water,
That brings forth its fruit in its season,
Whose leaf also shall not wither;
And whatever he does shall prosper.

4 The ungodly are not so,
But are like the chaff which the wind drives away.
5 Therefore the ungodly shall not stand in the judgment,
Nor sinners in the congregation of the righteous.

6 For the Lord knows the way of the righteous,
But the way of the ungodly shall perish.

Romans 6:23

23 For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.