You seem to be using "too ambitious" as a synonym for "unlikely to succeed". But that's something different.
"Too ambitious" implies someone shouldn't even be trying for this goal. That's a corrosive attitude, and I'd like it kept-in-check by a requirement that sources of such negativity show their reasoning/experience/work.
"Too ambitious" implies someone shouldn't even be trying for this goal. That's a corrosive attitude, and I'd like it kept-in-check by a requirement that sources of such negativity show their reasoning/experience/work.