If the above lines made sense to you, then only read the following paragraphs because I don't know if you can relate to this or not.
Learning quickly happens when you can know things quickly. That way you will have time to explore a lot and test a lot. Going through tutorials and documentation just allows you to know things. Therefore the quality of tutorials or mentors helps to grasp quickly because they just tell you what to know.
Real learning happens after you know things. Throughout my life, I got confused between knowing and learning. I can read or hear facts such that it allows me to recall the fact. But there were cases where I actually didn't understand the fact as I hadn't absorbed it completely. I just knew how things were but not the idea and reason why they were such.
When you want to truly learn something, to the finest detail, it really really requires a lot of effort and dedication. Picking up new skills is relatively easy. It just requires knowing enough to go through and solve your problems. But honing the skill to master level is really difficult.
Think about drawing sketches. You can just watch a tutorial on it and draw. Then close the tutorial and repeat it. You now know how to create at that pose. But when you want to change it, you will have to know about shading, pose, color, etc. Even if you know them, it's hard to use them because you may have never learned about them. Because to learn about colors, pose, shading requires experience and time. The more quickly you can iterate through it, the better you get about your preferences and style. Knowing them will only give you a shortcut. Learning them will give you a lot of creative freedom.