I am trying to find a word/phrase that describes someone who performs a "reality check" every time people suffer from misconceptions or over-exuberance. He/she is the "voice of caution" that prevents "fools from rushing in." A sage with a sobering influence.
What I'm looking for could be an eponymous adjective such as
panglossian (though obviously panglossian is nearly an antonym for what I actually want). It could be a noun - such as
Cassandra - if such a character personified the above traits. Any idiomatic expression or slang that might also fit the above criteria would also help.
The closest I have gotten so far:
I want to use the word/phrase in a sentence such as:
"I hate to be a
prophet of doom/
killjoy, but there is no way we can hit these goals in just a week!"