Although many attempts have been made to explain what life is, the high diversity of behavioral and structural properties of living creatures makes it difficult to formulate a comprehensive definition of life. Among the many signs of life, the one which seems truly ubiquitous is effort expended on maintaining the internal environment in living constructs independent of its surroundings. Stability of the internal environment is based on automatic regulation, which, in turn, depends on negative feedback. Manifestation of features produced by this effort is taken as the most specific sign of life. Hence, automatism of regulation differentiates living creatures from inanimate objects. The paper explains why regulation needs to be automatic, and discusses those attributes of automatic regulation which are particularly relevant in the context of life.