Please - for your health and the others around you - be happy. Please be happy.
Sit back and thing for a moment - when were you last at your happiest? Accomplished something at work? Do well on an exam? When you bought that new fancy contraption you've had your eye on? Whenever it was - think back to that feeling. Why did you experience that feeling? Why were you happy you accomplished something at work, passed that exam, bought that new widget?
Because you viewed it as a success. At that moment - you succeeded. Now, why can't we view every moment as a success? Every waking moment we experience - why can't that be seen as a success? Well lets start thinking that way.
I can't point to a specific time in my life to when I realized I needed to be a more positive person, I'm just stuck on how much it's changed my overall outlook on life. Maybe it was when I read the Paleo Diet book, courtesy of Joe Whisney, which laid out how much control I have over how I feel in life.
Maybe it was when I joined my gym and constantly surrounded myself with incredible people all working towards a similar goal - continuing to be awesome and kick the worlds ass. Or maybe it's whenever I look back at things I've been through and realize how happy I am with myself and how I wouldn't change those experiences - good and bad - for the world.
Always Find the Silver Lining
I yearn for the silver lining and go out of my way to find it. Silver linings are so often overlooked and yet are so key to keeping us going. Working in a creative environment, ideas get shot down. "We don't have the budget for this", or "they won't go for that," etc. However demoralizing those "no's" can be, or how embarrassed you might feel for pitching what others view as a bad idea - everything you've put into that decision making process is getting you to an end goal.
Sure - this is a very niche example, but I think you get my point. No decision is ever for naught. Each decision made, whether viewed good or bad at the time, is going to get you to where you ultimately need to be. And I find comfort in that.
So sure - life might suck, but it's sucked before. And it's probably going to suck again. But you've gotten through it once before and guess what, you're that much better for it.