Which of the following two statements is likely to produce a better result: "You need to stop making so many mistakes," or "I would like you to work on improving your accuracy?"
How about these two: "You need to stop criticizing people," or "I would like you to work on finding ways to praise your employees more?"
While it's tempting to use scare tactics or blunt feedback, positive-outcome statements tend to be more persuasive. (Researchers hypothesize that most people respond negatively to feeling bullied or "guilted" into changing a behavior.) So, if you're trying to create change, focus on the positives of that change. Take the person you hope to persuade to a better place instead of somewhere he or she should avoid.