I wish my attention span were shorter. Something uninteresting that wastes my attention robs me as surely as someone unprincipled who steals my wallet: cultivating a long attention span is as foolish as carrying large bills. True, there is little that does not interest me (or that I cannot imagine myself being interested in so vividly as to make it so). But even interesting subjects can be made uninteresting when their performance or exposition is occluded by mendacity, pretension, or false naivety. The ability to pay attention despite uninterest belongs to strength of character, not strength of mind, and is maintained at the expense of the intellect.
The hardest thing that eyes can do is stare. Precisely because our eyes are such efficient channels of information, the one thing they cannot do is settle passively on a single object. In fact staring is impossible. If the eyes were to stop moving, they would stop seeing; the principle of vision is not focus, but contrast. The possibility of sight depends on the continued tiny, restless motions of the eye called saccades: what the mind sees through the eyes is not the light that falls on them, but the contrasts in light which the saccades gather. Physiological fact is that to see is to look away.
Attention has the same principle. The harder you focus your attention, the narrower a channel your attention becomes, toward the asymptote of sleep. The more freedom you give your attention, the broader it becomes, the better it works. When you are rapt your attention is indeed rapt, trapped—not still, but caged; not pinioned to a subject but centered on it, pacing before and around it. All your instincts are for motion. When you look on a strange object, you walk around it. When you look on a beautiful face, you survey it in passes from eye to eye. The first thing an artist learns is not to stare. The first thing a thinker must learn is how to be distracted.