How to stop complain and start a new life?

If your enemy in company was been promoted, you would surprise why (s)he, not you? and  resent the injustice of the company's decision and fear (s)he would be not good for you.
You think that you are better and work harder than her/him, so you felt very bad when (s)he order you or assign some work to you. You complained to anyone, or pressed the feeling, then became more and more unhappy in work.
Resentment is  bad to your health and relationship of others. How to stop complain and peace the resentment.  I conclude the following methods from my life experience:

Knowing you are not do good thing for other's want you do

Chinese philosopher Laozi said:

知不知，上；不知知，病。
夫唯病病，是以不病。
聖人不病，以其病病，是以不病。 

It is great if you understand that you don't know that; It is bad if you don't know that you don't understand that.
If you know you are bad, you will not be bad.
Saint is not be bad because (s)he know (s)he is bad.

You complained that because you didn't know that you are not good for company. You should be peace and think that what is the company want you do(something help it achive its objectives). If the company want increasing income and you do something to double its income in a year,  I think the boss will promote you not (s)he.

Happy is he who is content
Laozi also said:

天下有道，卻走馬以糞；天下無道，戎馬生於郊。
罪莫大於可欲，禍莫大於不知足，咎莫大於欲得。
故知足之足，恒足矣。

When the world is in peace, we have time to let the horse to take a shit, but when the world is in war, the horse gives the birth on the road.
There is no more serious sin than desire, no more serious disaster than dissatisfaction and no more serious mistake than greed.
Thus you are always satisfied when you know you have had enough.

 When you complain your company, family and any unfair thing around your life, you can look down people who's status worse than yours. I always feel I'm so lucky when I see someone without a leg but work hardly.