Solomon once said that a man without self-control is like an unwalled city (Proverbs 25:28). In other words, such a person is easily conquered.
A lack of self-control is the chief weakness that leads to actual sinning. It is not a sin for Satan to suggest evil ideas to our minds. We are not accountable for what Satan does. Satan is an independent being. Our flesh (the pleasure-seeking part of our fallen humanity) naturally rises to the bait, the way my betta fish rises to the fish-niblets I drop into its bowl every morning.
But, we have not committed a sin just because we feel a spontaneous urge. As long as we live in mortal bodies we carry with us, and inside us, a desire for pleasure that triggers by its own nature. The question is, do I have any sort of inner brakes? My fish does not, because it is just a fish.
I don't mean that we need a better conscience, though that's usually true too. Paul's testimony in Romans 7 shows that he had a conscience. He agreed with God's moral laws, in his "inner man". Nevertheless, he confessed that there was some way (unstated) in which he could not stop sinning. Perhaps it was coveting, since he mentions that earlier (Romans 7:7-8).
Self-control is like a brake on a car. It's a scary thing for the brakes to go out. There are people who have no working brakes on their mouths or hands. Most people refrain from acting on their impulses because the Lord secretly helps them (I infer this from Romans 1, where it says the Lord "gives over" some people to their worst desires; so I gather the Lord must have been kindly helping before). But the lament of natural man is that we know what we ought to do, and we try but can't do it.
Our challenge as Christians is that our "inner brakes' are not consistent, and they can become stronger or weaker. We are new people in Christ, our hearts have sprung back to life, and we are indwelt by the Holy Spirit. But that particular fruit of the Spirit -- self-control -- has only started to form. Also, we are not machines. We don't punch out little widjets of holiness in a mechanically uniform way. We are more like plants in a garden. We're organic, so we grow unevenly. We might show excellent self-control toward one temptation (say, gambling), but repeatedly go skidding into a different temptation (say, boastfulness).
I commend to you the virtue of self-control, versus the moral flaw of being impulsive-driven. Self-control is not beyond our grasp. It is a supernatural virtue fostered by God in our souls, not merely a matter of gritting our teeth. The Spirit of God can build up self-control in us, even though it will require climbing mountains and enduring hardships. The self-controlled person is unconquerable.