Happiness. It's something we're all, in our own way, looking for.
The way you feel is mostly dependant on how you see things. Some things are more important and closer to you than others. Often, one bad thing is enough to bring you down, despite all the good. What you feel is a reflection of what you expected, what reality turned out to be and how you feel regarding that.
By this I mean that the way you feel is not an objective sum of everything going on, rather a subjective one (with additional limits and bypasses, which i'll simply just ignore. Ask me to elaborate if this bothers you). It is as if you weigh every factor (and often weigh the negative ones extra, even tho I'm still not sure why). Since this is entirely subjective (the smile of your crush might make up for this huge fight you've having with your best friend, or it might be the total opposite!), in a way, it can be rethought and re-evaluated. I also found that it often depends greatly on your expectations. If you expected things to go terrible, and they go 'okay', you'll be glad. If you expected an awesome day, and things go 'okey', you'll be sad. Did things go diffrent, or did you simply put up a diffrent standard to measure by?
While you often cannot control what goes on, you can control both your expectations and how you weigh reality. This leads me to conclude that ultimately, happiness is more of a choice than of a result of events in your environment. It doesn't matter how good or bad things are going on an absolute scale. Put any hungry little african kid in your place when you're feeling absolutely depressed, and they might just have the time of their life, just because from their perspective, your worries wouldn't matter.
It seems silly, happiness being a choice. Wouldn't we just choose to always be happy, then? Unfortunately, when you think about it, this is both psychologically and philosophically impossible (one cannot be happy 100% of the time, for happiness would lose it's meaning.) To me, this implies that no matter how good you get at controlling your emotions and happiness, you'll never fully overcome them (those who don't feel any emotions are not accounted for, they don't control, they simply don't have. Tho I guess that could be argued about). It does however help you control things, be happy more often and for less silly reasons, and whenever you're sad, in a way, it helps me cope.
So while we cannot maintain control over our emotions at all times, and choose and decide them to our likings, I do think we have a great deal of control over how we feel by simply manipulating and rethinking the things that bother us and focussing on 'the bright side'. As cliché as this sounds, I find that this works for me, which is why I guess i'll share it as an insight. (Not the most recent, but I bend and break rules to my own likings!
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PS : When and as long as we're happy, it doesn't matter what is actually making us happy, we just are.