This text presents an ontological inquiry into the subject as the primary source of activity and spontaneity. The author traces the development of human action from early infancy, where intentional activity and conscious goal-orientation emerge from the random movements of newborns. A central theme is the origin of this vital energy, which T. G. Masaryk defined more precisely as spontaneity. This quality is not a mere reaction to external stimuli but an autonomous initiation of action, for which the environment and the subject's own body serve only as tools or opportunities. The analysis demonstrates that the subject is not passively determined by external causes but actively responds to the world's challenges. In this way, the subject introduces new realities into existence that would not have occurred without its intervention. The work thus contributes to the understanding of subjectivity as a dynamic principle that transcends biological or mechanical causality, establishing the human being as a creative agent capable of altering surrounding circumstances.