One: increase and extravagance; to have more one needs. This addition is the way which satan uses to enter the heart. To protect oneself from that is to be careful not to fulfill the needs of the soul like food, sleep, pleasure or rest. Whenever you close this door, you would be safe from any enemy.
Two: negligence; Whoever remembers Allaah is protected by the fortress of remembering Him. When he neglects that he will be opening the door of this fortress and the enemy will enter. It would then be difficult to drive him out.
Three: Caring for what is not his business in all matters of life.