This paper is focused on the problem of the positive and the negative sides of being alone. Complex analysis of the problem includes philosophical anthropology, psychological personality theory, and psychometric data. Traditional views treat loneliness as a negative condition of frustration of the inherent sociality of human beings. This view is basically true but one-sided; the other side of the issue should consider the propension of personality development for internalization of social communications and shaping the inner world of auto-communication, or inner dialogue. This auto-communication creates the psychological basis of self-reflection. Solitude thus appears as an important resource that becomes salient only at a relatively advanced developmental stage. The theoretical model is supported by data collected using the new Differential Test of Aloneness (DTA) which embraces both negative and positive aspects of the experiences of being alone.