The self-preservation instinct, having its source in the sense of individuality, of separateness, is the motive of our self-assertion. It is necessary that each member of a herd should have a certain amount of self-assertiveness in order to maintain his place among his fellows. If, however, this quality is above or below the requisite standard, his survival will be endangered; if, on the one hand, he is lacking in self-assertion, he will not obtain his fair share of the means of life available for the group of which he is a member. On the other hand, if his self-assertion is excessive, it may disrupt the social organisation, and either lead to the extinction of the group, or to his ejection from it.
Lack of self-preservation instinct is usually due to deep-seated psycho-pathologies, too complex to be entered upon here; but we may say in passing that this failure is often due to a division of aims in the subconscious mind, the individual is not sure which self he ought to preserve, and so preserves neither.
An excess of self-preservation is often developed in the child who has had a hard struggle to find and express his individuality.
The self-preservation instinct has a great influence upon vitality. All observant persons must have noticed how easily the man who has lost his hold upon life, or has given up hope, succumbs to disease.