When you have a person complaining, let's say "This work is hard" or "Working with customers is dumbing", this person wants to make others do a job or things that her/him are supposed to do. Often, others can't cope with all that complaining, so they actually do it, instead of a person complaining.
Yet, we have to know a basic fundament of the Law of Attraction, and that is that what you focus your attention on increases. People often don't get this. They will say, "Yes, but I do affirmation every day to have more money", so if I focus on that, shouldn't I have more money. You can affirm (this is a very good thing to do) something consciously but don't forget unconscious affirmations. When you say positive affirmation 5 times a day, but you think negative 50 times a day, then your positive affirmation will never come to the fruition. You can not affirm "Money is easily flowing into my life" 5 times, and think or even say that you don't have money for this or that, or that you will never buy this, never have enough money, etc. Until number of your positive affirmations is not significantly higher than negative thoughts about the same thing, you will never manifest what you want.
Instead, a person that complains hundred times a day will be given even more things to complain about. She/he will attract endless reasons for complaint.
Many things we thought about our brain proved to be wrong. The brain can regenerate, can make new connections even in older age, brain cells are being created all the life, etc. Neuroplasticity is the ability of the brain to change itself. Self-help authors will say that our brain was created to be happy. But the reasons for mental diseases are in our negative thoughts that poison it and change it.
Scientists have found out that if we are complaining or being forced to listen to the complaints for more than 30 minutes a day, this will cause real structural damage on the cerebral level. If we consciously chose to turn obstacles into opportunities, we are improving the quality of perception and ability to find solutions.