Aren’t you just dying to tell someone at work they stink when they stink? A new study supports the idea of telling the truth to employees.

Oh, the management happy talk. Be supportive. Be collegial. Always give feedback with a positive spin.

Aren’t you just dying to tell someone they stink when they stink? Aren’t there days when you just want to storm into the office in some spit-soaked, David Mamet-Glengarry Glen Ross-fueled rage and shout “put that coffee down! That coffee’s for closers only!”?

Your time has come, my friend.

According to new research from Northwestern’s Kellogg School of Management and the London Business School, not only is giving phony encouragement to slackers a soul-withering experience for managers, it can also backfire and hurt the business. According to the researchers, an employee’s self worth gets wrapped up in the phony, esteem-boosting smoke you blow at them, which makes them try even harder to prove they’re good at what you really know they’re terrible at.

And then bad things happen.

“The more that people's feelings of self-worth are wrapped up in a poor decision they’ve made, the greater their impulse will be to justify it in some way,” says Daniel C. Molden, assistant professor of psychology at Northwestern and one of the authors of The Promise and Peril of Self-affirmation in De-escalation of Commitment.

Most of the study centered on financial and human-resources decisions. In one example, participants acted as senior managers and were given copious praise for their rational decision making. Now believing themselves to be world-class decision makers, they were then told that someone they had hired was not working out. An overwhelming majority recommended spending additional time and money on employee training, rather than admit they made a poor call and cut their losses.

Those who were given neutral or negative feedback about their overall decision making had no problem cutting the troublesome new hire loose.