Did you ever have a boss who only made her presence felt when something went wrong? Seeing her walk towards me down the aisle made me think to myself, with dread: "damn, what did I do now?"
If a person is only told his faults, he has to learn twice; once to unlearn the wrong thing and once to learn the right way.
As a coach, leader, or manager, it's constructive, and productive, to have a positive association with your people. Imagine if every time I saw this manager I thought to myself, "wow, I wonder what I did right?!"
Brown's Professor Barrett Hazeltine practiced this with passion. If someone shared something insightful in class, he'd race across the auditorium and shake the student's hand, stating: "that's really good", or "wow, you're really smart", in a caring and sincere manner. The student beamed.
In my professional career, associate Joe McCarthy was adept at telling people the specific, wonderful, pieces of their work or contributions. People spent hours with Joe.
In both cases, their offices looked liked deli stands, where students and associates lined up, waiting for insights and, I suspect, an opportunity to be praised. I don't think I ever saw anyone waiting eagerly to meet with my old manager.
If the right behavior is recognized and rewarded, it's likely to be repeated.
So, instead of finding fault, catch people doing something right. It will reinforce the desired behavior, and it will make the receiver's day. It's most impacting when the feedback is specific, timely, and reinforces a core value or goal.
It's easier to attract flies with honey. Have Fun!