This is the classic relationship between darkness and light; the ego and the universal consciousness. Rajas has this quality to change anytime between the higher Sattvic energy and the lower/darker Tamasic energy. The deciding principle in this interplay is one’s own nature or Prakriti (which includes body, mind, and spirit). Thus, every decision in diet, thoughts, and environment is an interplay between this darkness and lightness, or these higher and lower gunas. Effectively, we are creating the path as we walk along it towards higher or lower states of being.
Everyday we have the chance to be conscious of our choices. The foods we consume, the news we consume, the people we interact with, etc. all can play into the fluxuations between sattvic and tamasic qualities. If we are absentminded, we are at the sway of external forces. If we are grounded in our being, we can be conscious of the internal and external flow of events and thoughts, and actively choose to balance towards the sattvic characteristics of life.