Iris

'When everything feels like the movies, you bleed just to know you're alive'- Iris (Goo Goo Dolls)
Isn't this true? That just when life seems too good to be true, it falls desperately apart? When you are high and singing at the pinnacle of success, there will be that tiny sorrow which will drag you down? 
I'd like to think of it like too much happiness attracting negativity towards itself (just the opposite of what happens in Rhonda Byrne's The Secret) as a balancer. Isn't life about balancing- always- work and home, self and social, fat and thin- the Chinese even have a symbol for it- the Yin- Yang!
So you can never stay truly happy or woefully sad- it's a rollercoaster life. However, you can tune your attitude to reflect positivity and optimism- like finding the proverbial silver lining in each dark cloud.
We humans are a frightened lot. We seek safety in numbers, in trodding the common path and living a life of ease. For us, balance is second nature. 
Here's then, to positivity and some good cheer!