The secret of the whole matter is that a habit is not the mere tendency to repeat a certain act, nor is it established by the mere repetition of the act. Habit is a fixed tendency to react or respond in a certain way to a given stimulus; and the formation of habit always involves the two elements, the stimulus and the response or reaction. The indolent lad goes to school not in response to any stimulus in the school itself, but to the pressure of his father's will; when that stimulus is absent, the reaction as a matter of course does not occur.
Edward O. Sisson
In one sense the whole process of development consists of the formation of habits; for knowledge itself, and the powers of thought, as well as the higher elements in the will, all depend upon the establishment of fixed ways of reacting to given stimuli. Consequently, the general laws of habituation underlie the whole of education. But the term habit is more commonly restricted to those established reactions that act with little or no participation of consciousness, or, in other words, mechanically or automatically. Such habits as these begin to form very early, and constitute a kind of supporting framework for the higher elements of character.
Edward O. Sisson