These and other cliches are representative of our societal impression that life comes in cycles. We have a natural tendency to see varying events in the world as being cyclical, despite the fact that most macroscopic societal behaviors are, if anything, positive feedback, with slight advantages in (for instance) war snowballing into unstoppable divides. We see it when it is true, such as with the lunar and solar cycles, and we see it when it is false, such as with the perception of "hot streaks" in sports.
In recent months, I've devoted a fair deal of thought to a fundamental cycle in one's, or at least my, life. A few months ago, I remember distinctly feeling, and telling anyone who would listen, like the past period of my life had been one of self-improvement. I'd become more dependable as a person, I'd picked up some skills, and I'd reapplied myself to my vocation. Heck, I'd even lost those 10 pounds that had been bugging me since graduation.
I was frustrated, though, because none of this seemed to be paying off in any meaningful way. As the self-improvement has slowed and stopped, though, I've been happier and happier, even as I feel myself starting to slip as a person.
Maybe it's the inherent tendency to see a cycle in everything (hence the opening bit), but I don't think this is a coincidence. Self-improvement and happiness are the sine and cosine of life. Unhappiness spurs you to improve yourself, to look closely at your character and see what can be changed, what is causing the unhappiness. As you take those steps to better yourself, your betterment as a person naturally leads to success of the social variety, leading to happiness.
It's not without a price. When the happiness kicks in, the self-improvement slows down for two reasons. First of all, the happiness and approval justifies your current character, obviating the need for analysis and rejiggering. Second of all, because your position in life has improved, you find yourself spending more and more time doing and thinking things, which leaves you less time (and less incentive) to think about new things.
The self-improvement phase consists of thinking outside the box to expand it. The happiness phase consists of exploring the box and of figuring out what in the box you like; its ultimate denouement is the shrinking of the box to restrict itself to the chosen lifestyle. As the lifestyle continues, one ultimately gets bored of it; as one's friends move away either physically or via the personality drift that categorizes all pairs of people, the satisfaction also declines.
This leads to a relative bottoming out of happiness, as the self-improvement urge kicks in via Hooke's law. After some wallowing, one generally starts becoming more risk-positive, with less to lose, and exploring new facets of one's surroundings (both internal and external.) And so the cycle begins anew.
In this manner, I don't think the happiness cycle is an accident. When you're on top of your game, there is little reason to practice; besides, you're having too much fun to do so. When you're down in the dumps, you use your free time to gain a comparative advantage in improvement, which brings you back up.