A certain man wanted to sell his house. Another man wanted very badly to buy it, but because he was poor, he couldn’t afford the full price. After much bargaining, the owner agreed to sell the house for half the original price with just one stipulation: He would retain ownership of one small nail protruding from just over the door.
After several years, the original owner wanted the house back, but the new owner was unwilling to sell. So the first owner went out, found the carcass of a dead dog, and hung it from the single nail he still owned. Soon the house became unlivable, and the family was forced to allow the original owner to move back in.
The point of the story is this: If we leave the Devil with even one small peg in our life, he will be glad to hang his rotting garbage on it, and make our lives unlivable.