I think you guys are missing the point.
He's not saying suppress negative feedback, that is as important as any including positive feedback, that is as long as it is constructive.
The point is if you are "habitually" negative in a non constructive way. The phrase that really defines it is, "Some people confuse negativity with superior intelligence, as in 'I am cognitively able to find the hole in every plan.'" We all know someone like that. If you find yourself not able to be positive about anything then perhaps you are one too.
If you are a professional often time it's part of your job to find the downside in an endeavour. If you do that to make things better then you are doing your job, if you are doing it to tear things down your not.
