Thanissaro Bhikkhu wrote:
Try to notice when you look at something: Does your attention go flowing out? Do you lose your sense of the body? If you do, it's a sign that your looking isn't all that skillful. You want to be able to stay in the body as you look, as you listen, to maintain your sense of the breath energy throughout the body. If you can't, that's a sign either that you're looking for the purpose of forgetting the body — in other words, you're looking for the purpose of greed, anger, or delusion — or you're simply careless, and the sight, the sound, the smell, or the taste, whatever, happened to catch you off guard.
That's how most people look and listen and smell and taste and feel and think about things. They forget their inner center and suddenly find themselves centered outside, trying to get some pleasure from grabbing onto a sight or a sound and then elaborating on it — either to make it more attractive or to make it seem more meaningful than it actually is. If the mind is in a mood for a little bit of anger, you focus on the things that would provoke the anger and then you can elaborate on it, proliferate as much as you like.
Those are where our skills tend to be. We're great at proliferating. But if you think of input at the senses as a kind of food for the mind — which is how the Buddha sees it — you have to ask yourself: Are you preparing good food for the mind or junk food? Or poisonous food? That's the kind of cooking we're used to. We think we're cooking up great meals, but they can make us sick. So you've got to learn a new way to cook for the mind.
From: The Skill of Restraint
by Thanissaro Bhikkhu