I have been happy in the worst of times and cranky in the best of times, and vice versa. I can thus conclude that my level of happiness is a choice that comes from within me rather than being determined by outside influences. This is empowering. I can view life from the right angle no matter what is happening around me.
My right knee has been troubling me for a couple of weeks. I tend to get cranky when any physical ailment slows me down. I've been reminding myself that "this, too, shall pass." I have an appointment with an orthopedic doc to check it out. In my mind, it's a big, annoying, happiness-dimming deal. Then last evening, I saw in an MLB game a horrific collision between two players that left one with a career-threatening leg injury. That quickly gave me the "right angle" to see that my knee issue isn't that bad.
Both happiness and unhappiness can gain momentum within us. I lean toward happiness just because it feels so much better.