In my opinion, this sentence can also be understood from the perspective of learning.
When we first came into contact with new knowledge, we were very strange to it, and we didn't understand why it was like this and why it needed to be done. The only thing we can do is to imitate, learn from the experience of our predecessors, imitate and master its basic principles.
At this moment, the pen in your hand begins to turn.
After a long period of practice and accumulation. At this point, you seem to gradually understand the principle and why you need to write like this.
But as you know more about it, you will find a new continent, a new continent derived from it, a new field that is familiar and unfamiliar.
This is when you are familiar with a certain knowledge point, another knowledge point is derived, which is endless, thus forming your knowledge system and your research field.
All this requires you to turn the pen in your hand. Only after you master the operation can you understand the truth.