I'm sure "flourishing" or "happiness" can be defined by social psychologists and to some extent studied empirically. There has been a lot of research on human happiness in the last few decades. Jonathan Haidt discusses exactly how social scientists look at human happiness in his book, The Happiness Hypothesis. Social scientists quantify and measure human happiness by first establishing various definitions and assumptions about how we measure happiness. Such a discussion must include the latest science on the how the human brain functions. And Haidt also looks at different personality types to see which are more apt to experience happiness.
To be sure, the social sciences are only way to look at human happiness (flourishing). Philosophers have been looking at this from the dawn of time. There are metaphorical ways of examining and exploring human happiness through poetry and imagery that elicits feelings. The Buddha had a lot of ideas about human suffering and human happiness that are still relevant and amazingly compatible with a modern scientific understanding of the human brain.
Here's a passage from Haidt's book that introduces the idea of a happiness hypothesis . . .
Buddha, Epictetus, and many other sages saw the futility of the rat race and urged people to quit. They proposed a particular happiness hypothesis: Happiness comes from within, and it cannot be found by making the world conform to your desires. Buddhism teaches that attachment leads inevitably to suffering and offers tools for breaking attachments. The Stoic philosophers of Ancient Greece, such as Epictetus, taught their followers to focus only on what they could fully control, which meant primarily their own thoughts and reactions. All other events—the gifts and curses of fortune—were externals, and the true Stoic was unaffected by externals.
Neither Buddha nor the Stoics urged people to withdraw into a cave. In fact, both doctrines have such enduring appeal precisely because they offer guidance on how to find peace and happiness while participating in a treacherous and ever-changing social world. Both doctrines are based on an empirical claim, a happiness hypothesis that asserts that striving to obtain goods and goals in the external world cannot bring you more than momentary happiness. You must work on your internal world. If the hypothesis is true, it has profound implications for how we should live our lives, raise our children, and spend our money. But is it true? It all depends on what kind of externals we are talking about.
Interestingly enough, Haidt discusses some of the evidence that suggests that people who hold "pervasive positive illusions about themselves, their abilities, and their future prospects are mentally healthier, happier, and better liked than people who lack such illusions." I always tell my wife that she suffers from positive bias (a real thing). Though I'm more pessimistic by nature and probably less happy, I'm probably better than her at seeing the world as it really is.