Holy @#$%^! ... I have never seen such a simple graph explain so much about life. There are so many things I could think of that would prove your graph right, but I'll just highlight a few standouts...

• The popularity that many idle/incremental/clicker games have enjoyed over the last few years seems to be rooted in the fact that the well-designed ones try to always keep players and their gameplay "in the flow". So players go [on the graph] from A1 to A4 and beyond as they progress through these games, and many get addicted as they find it hard to quit because they're always able to stay in the flow.
• In my own profession, there are many folks (including myself) who are in that A2 zone. But I suppose that this would hold true for any job that is largely a grind (show up, do your thing competently, get paid) -- whether someone is a video poker player or a Walmart inventory checker or anything in between, if you grind for a living, you will get A2'ed eventually.
• More specific to gambling in general, there's the professionals in the A2 zone, the flow zone populated by those few folks who were lucky enough and smart enough to win a life-changing sum of money in one shot and then quit, and then everyone else (well, more like 95%+ of everyone who ever gambled) over in the area between A3 and the y-axis. Which for me, is close enough to a saying that I keep hearing that of all the folks who try to make it at gambling, only 1-2% succeed, another 8-9% break even or come out slightly ahead, and everyone else (the other 90%) ends up a net loser.

This is definitely one of the most fascinating reads that I've found on Steemit. Now I do have one question I'd like to ask... you mention that the brain needs stimulation and cite games, alcohol, and drugs all as potential sources of that stimulation. Does that imply that because of this need for stimulation, every human is likely to end up with an addiction to something at some point during their lives, and why or why not?