Man, I just learned to compliment actions rather than talent, and now I have to do it the other way around. I get why, though. Moral actions are choices. Being smart isn't. If you praise a kid for being smart, he won't be able to choose to be smart. Instead, he'll assume he's smart and won't have to work so hard. I suppose praising an innate tendency to work hard might be more effective.
This sort of gets coupled with the idea of 'work smarter, not harder.' When a child is praised more substantially for trying hard, you get things like staying up all night studying for a test. When you emphasize being smart and not needing to study, the child is more likely to push themselves such that they can land good grades without needing to study.
And this usually manifests as greater attentiveness in class, greater emphasis on figuring out exactly what's going to be on the test, etc. But you also see behaviours like emphasizing getting the right teachers.
And the same thing applies to sports. If you emphasize effort, you might get a child practicing repeatedly something that they are already good at. When they are really bad at passing, you get thought patterns like 'at least I'm trying.' When you emphasize being good, the child is more devastated by the idea that they are bad at passing, and they focus their energy on being not bad.
The point is that things like being 'smart' and being 'good' are things that you can actually learn, and a lot times, working on what's important is much more important than the overall volume of effort.