First and foremost, what is positive psychology? Positive psychology studies what enables an individual or a collective group – be it an organization, party, etc. – to thrive and flourish.  Positive psychology ensures the positive thriving and flourishing of the individual or individuals in question and guarantees that such entities function optimally. The term ‘optimal functioning’ is prevalent when talking about positive psychology. In a nutshell, positive psychology is the broad study of well-being.
When individuals become more positive in their actions, inactions, and outlook on life, they are identified as having positive well-being. And this summarizes what positive psychology stands for – the study of what improves the quality of life by cultivating life-improving habits. 
Positive Psychology: A Modern Shift from Negative Mental Attributes
Psychology witnessed a radical shift in the 20th century. This radical shift was from the study of negative mental attributes to positive mental attributes. The beginning of the 20th century saw war, resistance, and epidemics, such as World War I, World War II, and the 1918 Flu pandemic, amongst many others. The lives of ordinary people were affected due to death, depression, and grief. The world was in turmoil. At this time, psychology primarily focused on adversity, horror, and doom and gloom. 
After a copious foray into exploring and projecting negative mental health attributes (not excluding depression, violence, irrationalities, and other tragic manifestations), a new and radical trend began to bloom. This new movement serves as a countermovement to negative psychology. It deemphasizes negative mental attributes and prioritizes positive attributes, such as kindness, happiness, civility, strength, and courage. All of these positive mental attributes are central to the goal of optimal functioning. The history of positive psychology even pre-dates the manifestations of negative psychology, as it is traceable to the works of Williams James in 1902. The writer was the first to coin the term “healthy-mindedness.” It was not until 1998 that positive psychology became entrenched within the psychology community. Martin Seligman, the head of the American Psychology Association, thematized positive psychology during his tenure. Such is the historical evolution of positive psychology as a field.
How Can Positive Psychology Reinforce Positive Wellbeing?
Since positive psychology dwells on the well-being of an individual or group, the feeling of such positive emotions can be considered subjective. Positive psychology can be split into layers. Since a human being’s experiences revolve around all timeframes, the positive experiences are not limited to the present. When reflecting on the past, they are not distraught but satisfied. In the present, they are constantly luxuriating in happiness. And when they envisage further into their future, a positive feeling of optimism overwhelms them.  Thus, feelings of positivity in the ‘then,’ the ‘now,’ and the ‘later’ capture the totality of a well-rounded discourse on positive psychology.
The above explanation answers how positive psychology can reinforce positive well-being. The explanation shows that when feelings of positivity have been displayed in the past, those same feelings are displayed in the present for the sake of the ‘now’ and ‘later.’ Such positive psychology is wholesome to one’s well-being.
Positive psychology emphasizes the positive mental, physical, and psychological well-being of an individual or group of individuals. This does not mean that an individual with positive well-being will no longer experience feelings of anxiety or sadness. It is only human to experience the sober aspects of life. What distinguishes an individual who experiences positive well-being and one who does not is that the latter can find themselves submerged in feelings of negativity. At the same time, the former – the positivist, so to say – overcomes such negativity and embraces positive psychological traits.
Shelly L. Gable et al., What (and Why) Is Positive Psychology? Review of General Psychology, 2005; Vol. 9, No. 2, 103–110 DOI: 10.1037/1089-26126.96.36.199
Michael M. Prinzing, Positive psychology is value-laden—It’s time to embrace it, The Journal of Positive Psychology, 2020; 1-9, DOI: 10.1080/17439760.2020.1716049
Martin E.P. Seligman et al., Positive Psychology: An Introduction, American Psychologist, 2000; Vol 55. No. 1.5 14 DOI: 10.1037//0003-066X.55.1.5