Toni, I agree and disagree with some of this, I think it's more a case
of the person having to look at what they see as negative and why. Quite often the task within any team is for one person or group to look for the problem while another looks for the solutions to those problems, that's because people think differently.
Failure to see the downside of any issue has caused more problems and project failures than any person being negative about it. That's so because not seeing the pitfalls early ensures you fall in them when it's too late to rake any evasive action.