This has been scientifically proved wrong. Sonja Lyubomirsky writes that people come with innate levels of happiness, and apart from temporary swings (in either direction, in response to life events and activities), and apart from hugely intrusive, foundational trauma, "level of happiness" tends to remain constant for any given person's lifetime, and said level covers a huge spectrum, when viewed across people.

You can train your mind and habits to increase your happiness, but still, in her famous book, she assigns 50% weight to what level you are born with, and says that, however you fine-tune yourself only amounts to the other 50%. And, since her book was published, more recent research assigns an even higher weight to the innate level of happiness (i.e., higher than 50%). The sun does shine differently on different people, and it's not a mental health issue, it's just a given.

Think about it: if someone is born with 100% happiness, and never thinks consciously about their own happiness level, they will still be more happy (1 * 0.6 + 0 * 0.4 = 0.6), roughly speaking, than a person who is born with 0% happiness, but does everything in their power to improve (0 * 0.6 + 1 * 0.4 = 0.4).

> If you find yourself unable to be consistently at least /neutral/ in a first world country[,] that tends to be a mental health issue worth addressing.

I do agree about this; just know that the playing field is not level at all, and people who are less than moderately happy most of the time are not outliers; they are frequent.