"A man without self control is like a city broken into and left without walls."
Walls were important for cities in the ancient world. Walls were built around the entire city, even the largest cities. Walls provided protection from the attacks of enemies. The pride of a city was its walls. A city that was without walls was in a very vulnerable position. Every enemy could walk in the city without much of a fight. They could plunder and kill as they liked. Without walls, there was no defence against an attacking force. Such a city was a disgrace--like Jerusalem in the days of Nehemiah. Walls are important to a city as self control is to people.
We need self control. Without it we are defenceless against the assaults of the devil. Every temptation that comes our way will ruin us even more. How many people are ruined by a lack of self control! Drunkenness ruins lives and families. Not controlling the impulse to buy leads to debt and bankruptcy. Sexual desire unchecked destroys and plunders thousands. Much more could be said of a failure to control anger, appetite for food or sleep, our words, and so on. In our fallen condition man is not born with self control. As such sin has mastery over us. We are under the power of sin. We are defenceless against sin. We have no self control. We are a city in ruins and in disgrace. We need God to come down and fix us up.
One of the fruits of the Spirit is self control. Gal 5:23. The Spirit is given to us when we are born again. He gives us the power to exercise self control in all things. His infinite power helps us to defeat sin and temptation. His power working in us is like a wall that protects us from giving in to the desires of the flesh. When we live in dependence on God's power and follow the truth of His Word, we will be able to defend ourselves against the desires of the flesh. So if you lack self control, cry out to the One who can help you. He can give you the strength to control your passions, lusts, appetites, and thoughts. Then we can train ourselves for godliness. 1Tim 4:7.
To put the proverb another way, a man with self control is like a city surrounded by a strong wall with a defeated enemy lying outside the walls.