There are times when you might wish that you could change someone, but the only person you can have absolute control over is your own life.
"There's only one corner of the universe you can be certain of improving, and that's your own self."
"Our attitudes control our lives. Attitudes are a secret power working twenty-four hours a day, for good or bad. It is of paramount importance that we know how to harness and control this great force."
The only thing complaining does is to convince other people you are not in control and that you let less than positive circumstances control your mood and outlook.
"If you don't like something change it. If you can't change it, change your attitude. Don't complain."
"When you consistently maintain a positive frame of mind, you'll become known as a problem-solver rather than a complainer. People avoid complainers. They seek out problem-solvers." Joseph Sommerville, PhD
When you think you cannot succeed then this is what the mind will believe. So, invest in your own confidence and change your mind into a positive resource.
"Believe that you will succeed, and you will."
"Believe in yourself! Have faith in your abilities! Without a humble but reasonable confidence in your own powers you cannot be successful or happy."
Norman Vincent Peale