The realist

A diplomat has given up on the ideal out of mature readiness to see compromise as a necessary requirement in an imperfect world.

The diplomat may be polite but is willing to deliver bits of bad news. We should say that they're fired, that their pet project isn't going ahead, but instead pretend there is a glimmer of hope. Real niceness means helping the people we are going to disappoint to adjust as best we can to reality. The diplomatic person administers a clean blow and kills off the torture of hope, accepting the frustration that's likely to come their way.