That moment when you bring up concerns with an idea and your colleagues say you need to think positive. :P

This actually happens quite a bit in the corporate world. Have the ++.

There are 10 degrees of positiveness. Being optimistic, and blindingly positive. If you are just optimistic, then you consider other ways to stay positive. In other words, you PLAN your way out of trouble you are in. If you are blindly positive and hope that everything will be fine then you will be buried with the issue you are having. It seems like your coworkers are trying to force the latter idea into you. When something like this happens ask them if they any SPECIFIC reason why you should think positive. If they don't, then you can ignore them don't give into the PEER PRESSURE!

Get feedback training. You can still be negative but they wont see it that way

This used to happen to me a lot and there's nothing more annoying. It's called rose tinted stupidity and is much practiced by moronic software salesmen who don't want to be told that our product doesn't do something they've already told a client if can do because it might stop him getting the sale.