Happiness is a state of mind or feeling characterized by contentment, love, satisfaction, pleasure, or joy. -Wikipedia
Life is interesting and complex. There is a whole spectrum of experiences that come with life - good, bad, happy, sad and anything in between. It is this array of experiences that make us who we are.
As annoying and frustrating as down times are, they are not the be all and end all, in fact they are needed. After all, there is no meaning to 'perfect' if there is no imperfection. Happiness holds no meaning if there is nothing to complement it. This is not to say that we should always dwell over problems and sorrows; instead we should be optimistic and try to see the brighter side of things whenever we can.
There is always plenty happening around us, often so much is happening that we cannot acknowledge them all. So, be selective and concentrate on the ones that make you happy, the ones that you like. There is always bound to be something good that is happening; so don't go and make your life harder by looking at those that irk you, because as unfortunate as it is, they often come and find you instead. When they do find you, don't give up - smile, be brave, be optimistic - it won't last forever.
Being happy is one of the most important things in life. As much importance as society today places on material wealth, it doesn't matter how much material wealth you have, they don't mean much if you're not happy. Life is too short and precious to be wasted on our worries, so instead go and find something that you enjoy doing.
Smile, be happy :)