Like a city whose walls are broken down is a man who lacks self-control. (Proverbs 25:28 NIV96)
A city that never comes under attack from outside forces has no need of walls. We only build walls to defend ourselves from the enemy. When we lack self-control we allow the enemy, in whatever form it may be, access to our hearts and lives.
Self-control could be defined as having the ability to do something but choosing not to do it for the sake of a higher purpose.
Consider today what part of your life you need to defend from the enemy. Secure your walls with self-control. Discipline yourself in that area through small steps and stages. Like a wall being built lay a solid foundation to build layers of protection upon. Engage a friend for help and encouragement. Walls protect a city and no city has but one inhabitant.