1. People who know things and never speak up about them
2. People who don't listen when someone speaks up
Let's discuss each one and figure out how we can avoid ending up in the "I told you so" situations.
I've been thinking about this ever since the JC Penney's Super Bowl tweet debacle. The "tweeting with mittens on" campaign was perhaps the single worst idea ever conceived. Despite how much "engagement" it received, it was terrible. I imagine that in this meeting one of two things had to happen. Either there was a junior staffer that thought to themselves, "WTF, this doesn't make any sense," but said nothing. Or there was a junior staffer who said, "Hey guys, this doesn't make any sense," who was ignored by the social media team lead.
I only say this because I've sat in meetings that have gone this exact way. We come up with a terrible idea, our intern knows it's terrible and then waits till it fails before telling us it was terrible. In my time, I've had one intern who wasn't afraid to speak up about how awful an idea was. That intern has ended up doing pretty damn well for themselves. The ones who hold it in and wait till an idea fails before saying anything... well, just stop it now.
But, the worst people on the planet are the senior and director level (and up!) employees that know all and discount any other ideas. It's remarkable to witness a upper level employee not listen to the people they've hired. I'm baffled when I'm in collaboration meetings and the leader has no intention on collaborating. They have their tactic and the sole purpose of the meeting is for everyone to agree with them. They will often become combative when team members disagree. It's difficult to harvest creativity when you stifle your team's ability to contribute. More importantly, you're going to have to find yourself hiring a new team sooner than you anticipated.
So check yourself before you wreck yourself. If you want collaboration then spark an idea and allow your team to ignite it. You hire employees because you believe in them. If you don't believe in them, then get rid of them and find new ones.
And, if you want to move up in your company, then speak up and contribute.