If you’re not convinced about the value of being grateful in life, you can try looking at the opposite side of the coin. One simple way of doing this is thinking of negative speech and its effects on a person.
If you’ve once been said that you’re fat, your clothes are ugly, or your work is below standards, how did you feel about yourself and about that person who said that? And if you’ve been overly critical of a person even just once, observe how that person relates to you. Does he feel at ease when talking to you? Or has he also been critical of you just the same?
A critical attitude definitely opposes an attitude of gratitude. It hinders blessings and ruins relationships.
Even the great writer and lecturer of self-improvement programs, Dale Carnegie, has his share of receiving negative feedback and how it hurt him badly. This article on Self-Help Daily features a story by Carnegie on this subject - Criticism of Others.