Two children have just completed a task. Both are praised for completing it.
Child 1 hears: "You're so smart, good job!"
Child 2 hears: "You did such good work, good job!"
They feel roughly the same, but there's a substantial difference. Consider the implications:
Child 1 hears: "You have an innate ability that allowed you to complete this task."
Child 2 hears: "You did a lot of work that allowed you to complete this task."
Now do you see the difference?