Thank you @timotto - I would say that when Eve believed the serpent’s lie, that corrupted her mind; when she desired the forbidden, that corrupted her heart; when she chose to disobey, that corrupted her will, completing the pollution of her soul by the sin nature that now dominated her. And when she swallowed the fruit, that corrupted her flesh - making her sinful both inside and out.
Adam too, for similar reasons that are open to discussion.
And they passed that corrupted nature down to all their offspring.
So if you’re asking your question about the sin nature relative to a lost person, then it would not just be the unruly appetites of the flesh alone. Paul says in Ephesians 2:3 that when we were lost, we fulfilled the desires of the flesh and of the mind. The “mind” in this case is what he calls the “carnal mind” in Romans 8:5-9. It’s the mind of a lost person that is fully “on board” with gratifying the flesh.
But if you’re asking relative to a believer, then I’d say you’re on to something. When any of us reject the lie and believe the truth, when we detest our sin and hunger for righteousness, when we choose Christ and deny self, the gospel reverses the curse on the inside. The Spirit replaces the inner sin nature making the believer a saint.
He is no longer on board with the flesh. The Spirit within him strives against the flesh to control the will and submit to God - and he grieves over sin even as he gives into it. The spiritual mind serves God - Romans 7:25. Sin vexes the righteous soul - II Peter 2:7-9. Salvation ruins a man for sin!
So then, why does he still do it? The biggest reason is what you’ve brought up. Of course there is wordly pressure and devilish disinformation - but the “unruly appetites” of the fallen flesh are the thing that Paul seems to confront the most. You see it in Galatians 5:17 which is just a condensed version of Romans 7:14-25.
I believe that the reason genuinely born again Christians sin is because of weakness, not wickedness. That was why the disciples slept in the garden while Jesus prayed - their Spirit’s were willing to watch with Him, but they were weak to the flesh. That’s what Paul is describing in Romans 7 - the power of the flesh taking advantage of our spiritual weakness. The Bible absolutely never uses the word “wicked” to describe Christians. But it does describe us as weak often enough.
And by “the flesh”, it means everything material about us - everything made up of atoms - the body and all its juices - including the enzymes and secretions, the chemicals and hormones that affect our moods.
Your Spirit wants to be at peace, but someone makes an insulting comment, and your flesh churns out adrenaline that makes you want to swing a fist - and your Spirit starts saying, “No flesh! Down flesh! Bad, bad flesh!”
Your Spirit wants to be pure, but some bikini babe goes bouncing by, and your flesh churns out hormones that disturb your thoughts - and your Spirit says, “Bad flesh! Down flesh! No, no flesh.”
The Holy Spirit living in you will never be okay with sin. Your flesh will crave sin until the day you die - but your Spirit? Never! Because it is absolutely holy, and it will always long to be free of sin.
A gazillion eons from now, the infinitely Holy Spirit within you will be no holier than it was the day you were born again - but in your sinless and glorified body, it will finally be free to express the absolute holiness it has always longed to!
I hope this addresses what you were asking.