My personal experience says it is a question of visualizing and focusing.
If I visualize not eating a delicious chocolate chip muffin with a lump of cold sweet butter on it, the picture that comes to mind is a delicious chocolate chip muffin with a lump of cold sweet butter on it. I am apt to be attracted by that image
If I am an archer trying to hit a target with rocks in front and a swamp in back, and I am fearful of losing or destroying an expensive arrow, I better not focus on avoiding the rocks and the swamp. My only hope is to focus on the target -- in fact, if I can narrow my focus to the center of the target, that is even better.