Training of the Happiness muscles

Happiness is mental state of mind. 
We all know that, but how to achieve that state? This is the question.
 

Recently I found out a very interesting material about that idea.  
The state of mind is like muscle - you have to train it. At the beginning your happy state is not so strong. If you are untrained you cannot stay happy for longer period of time (e.g. 4-5 hours). And if you do it you will feel tired after that and need to go back to your usual state. The solution is to train that happy state every day through activities that makes you happy.
Like every training after some time you will get easier in this mental state and you will be able to stay longer in it.
It was also mentioned that also your neurology would change and allow you to generate more “happy” hormones like endorphin.
 

Good luck with the training and be happy!