The distinctive thing about a state of mind such as that just described is that the focal object is much clearer than the marginal objects. For example, when you fixated the letter O, it was only in the vaguest sort of fashion that you were aware of the contact of your clothing or the lurking ideas of other lessons. As we examine these marginal objects further, we find that they are continually seeking to crowd into the centre of attention and to become clear. You may be helped in forming a vivid picture of conditions if you think of the mind as a stream ever in motion, and as it flows on, the objects in it continually shift their positions. A cross-section of the stream at any moment may show the contents of the mind arranged in a particular pattern, but at the very next moment they may be arranged in a different pattern, another object occupying the focus, while the previous tenant is pushed to the margin. Thus we see that it is a tendency of the mind to be forever changing. If left to itself, it would be in ceaseless fluctuation, the whim of every passing fancy. This tendency to fluctuate comes with more or less regularity, some psychologists say every second or two. True, we do not always yield to the fluctuating tendency, nevertheless we are recurrently tempted, and we must exercise continuous effort to keep a particular object at the focus. The power to exert effort and to regulate the arrangement of our states of mind is the peculiar gift of man, and is a prime function of education. Viewed in this light, then, we see that the voluntary focusing of our attention consists in the selecting of certain objects to be attended to, and the ignoring of other objects which act as distractions. We may conveniently classify the latter as external sensations, bodily sensations and irrelevant ideas.