How Much Can Someone Improve Their Happiness?

When i was a graduate student, i was running studies all the time and reading hundreds of scientific papers. And one of the things i noticed is that psychologists were trying to make claims about how much people could change and grow based on these scientific studies. But very few things in our lives are influenced by only one little factor. Rit everything is connected. So if you're interested in understanding how much can somebody improve their happiness, or how much can someone improve their focus, you would need to take an approach that's a little bit more multifacited than that.