Exercising an emotional muscle "Gratitude"

It is often said that "gratitude" is very important for relationship in many kind of self-help books. I try to keep it mind but often forget.

I found an article, which says that  if you want to be successful, you need to feel more gratitude, and you can exercise your sense of gratitude like a muscle.

The article is here;

http://www.inc.com/geoffrey-james/gratitude-true-secret-to-success.html


It seems to be how to develop positive thinking rather than how to develop gratitude.

Anyway, I try doing it.