Growing age and bad thinking one of the main cause to feel unhappy or frustrated. Human brain is like computer ram or hard disk that can store lots of memorable day that had been happened in your past life.By growing age , you are storing more and more memorable history in your brain and your brain function working more and feel more stress to work more side. Such example,The child love to play with pleasure when they work or play they always be happy mood and full of concentrated mood in one work but one major income source father who do lots of work from office to home needs lots of thinking in one time. One time , when you handle lots of work by yourself you must feel frustrated and when you are not success in you plan then you also be feel frustrated.
May be, life is totally war place whey you are only solder must join in battle place but you want happy how it is possible?.
Happy means you are working your work normally no limitation whatever you want for your desire life from girl friend to money everything you have but human expectation no have limit that is why your limit of desire may could be feel you happy.
One of the main reason to be unhappy is , i personally believe is love affection, where you are full of empty from true love that is really rare found in the earth.
Love connection may could help you more than money in the earth but love depends on two people love each other but two person love each other so rare that is one of the main reason most unsuccessful unhappy man.
Busy life and cheating with life partner or lover may one of the cause to be unhappy so do not cheat who loved you or make commitment for your lover staying with him or her forever.