When you say the word “but,” you alert people to their failures. This causes them to focus on their failures and become demotivated.
Alternatively, if you concentrate the person’s focus on their success and indirectly alert them to their failure, they will be much more likely to correct their mistake.
Praise people for what they do right by not saying “but.”
For example, instead of saying, “I’m glad you worked hard, but, you could have done better,” say, “I’m really proud of how hard you’ve worked, and if you continue to work this hard, you will only continue to achieve better things.”