Why is it that a person who's mind is set on the flesh cannot please God and cannot do good? Because they are compelled by their inner being (which is opposed to God) into outward actions (which are opposed to God).
Jesus, in rebuking the Pharisees for their words against his casting out of demons said this:
"Either make the tree good and its fruit good, or make the tree bad and its fruit bad, for the tree is known by its fruit.34 You brood of vipers! How can you speak good, when you are evil? For out of the abundance of the heart the mouth speaks.35 The good person out of his good treasure brings forth good, and the evil person out of his evil treasure brings forth evil.36 I tell you, on the day of judgment people will give account for every careless word they speak,37 for by your words you will be justified, and by your words you will be condemned."
What does this mean for our man who lacks the spirit and has his mind set on the flesh of Romans 8? He is unable to please God. Out of his heart, which is set on the flesh, he brings forth evil treasures.
Notice that this amounts to pretty much a complete denial of the popular conception of free will as man having some autonomous choice. Instead of being free, our wills are bound by our nature. We were "dead in our transgressions." We were slaves to sin. Given the choice to serve God or serve Baal, we choose Baal, every time, because that's what our hearts were set upon. Thus we're unable to please God in thought (minds set upon flesh) and in deed.
Some previous posts on this/related topic:
Defining free 1, 2, 3
More on free will