This text explores the ontological issues of beingness, certainty, and existence, defining every true being as a happening unity bounded by its origin, progression, and demise. The central question of the reflection concerns the basis of our conviction that a particular being truly "is" rather than being a mere fleeting illusion, vision, or deceptive sensory perception. The author argues that the key criterion for beingness is a certain duration in time, which allows us to contemplate and speak of the subject as something constant. It is precisely this temporality and eventual occurrence that form the necessary basis for distinguishing reality from mere appearance. The reflection emphasizes that being is not a static state but rather a dynamic process whose identity is maintained through its temporal course. In this conception, the study of beingness necessarily becomes a study of time and the internal unity that connects the beginning and end of every existing thing into a single holistic and meaningful whole, the existence of which we can be certain of based on its persistence in our perception and thought.