Defining Moments portrays the consequential split-second moments of our lives that definitively impact our foreseeable future in hardly reversible ways. In part of the works, Greatjoy frames the idea as great epiphany moments. In other pieces, he expresses the defining moment through the physical manifestations of the subject's body movements.

 The series approximates the saying, "Good things take time, Great things happen all at once" - and applies it in both ways, "Bad things also take time, and tragedies happen all at once". The defining moments of our lives lie near these two extremes.

Within this framework, Defining Moments encapsulates momentous successes and the noxious blow of crushing defeats realized within a small window of time, bearing far-reaching consequences.

Depicting these climactic moments has always fascinated Greatjoy - the point at which one psychologically savors imminent victory, and the opposite, moments in which one is haunted by the sense of a devastating looming tragedy.