> a rep as a negative person if you make _true_ predictions
> out-loud that don't fit the common desire.
I've heard this very often, both as advise, complaint and even in an intimidating manner. And yes, I've seen this, people who stay kind of positive stay in their position even if they screw up a project completely so it has to be "rebooted". In fact I've also observed a super negative person, being a colleague of mine for 2.5 years and staying good with everybody despite one screwed up project.
On the other hand people have put me in various settings under high pressure to keep my mouth shut both internally and externally. (That was only in the startup/co-founding setting though.)
My conclusion: I'd take this advice with a biiiiiiig grain of salt. In my experience people get away with everything as long as they stay confident and keep their shit together.
Disclaimer: I'm not a team lead