A common adage in our coach's office is that you don't complain in front of athletes, because if you complain, they'll complain about the same things. If you must be negative, you do it behind closed doors where they can't hear you vent.
It's not a far stretch to suggest that you shouldn't complain in front of your co-workers either. Same reason. Exchange enough complaints and soon you can't tell where your beliefs came from in the first place.
We each have a sphere of concern -- things we'd like to see change but can't control. We each also each have a sphere of control -- things we can change immediately. Usually there are enough tasks in the second sphere to keep us busy for several lifetimes.
Which sphere you focus on dictates which sphere everyone around you focuses on.