HOW do you get good grades with just 3-4 hours of studying/ work a day?

So I've seen a lot of posts from people saying things like you can get good grades from 3-4 hours of studying a day. HOW?! I've tried doing this, and I can only cover like half of the material I need for the course. And it's not like I'm spending extra time on things I don't need to (like I'm not spending extra time on my coding programs if I have exams coming up, nor vice versa). It just seems like nobody has any information on this topic and it's really frustrating.