Another great article @leighrubin.
One sentence I've heard that ties in with this is that it is our job to fail, but to fail fast. Once getting to the heart of a problem, we ideate with the knowledge that we have and go from there. Everyone makes mistakes, but it is how you deal with them that earns the trust and respect of your workmates. I completely agree with your statement of "offering up a solution". Or even many solutions. No-one responds well to someone that comes up to them, tells them bad news or that something isn't going to work, and then don't give them options.
Another statement that ties in with this and being confident, is that UX is a blinking tough job, because everyone can see and comment on what we do (i.e. developers, sales, higher level managers). Everyone has an opinion, so the next skill is being able to say thanks to them for letting you know (without letting them get to you), collate all of them, use your knowledge of why the decisions were made in the first place to filter these down to things that could be tested or possibly improved on later.