Answer: C. Always focus on learning one thing well.
Step-by-step explanation:
The master is essentially telling the student that it is better that they master one thing and become very good at it such that they can utilize it effectively or at the very least, one should learn a skill first before they can then go off to another.
This is the very concept that has driven human innovation. Because humans have focused on various fields, they have been able to push those fields much harder than had they focused on multiple fields.
For instance, Pharmacists focused on medicine and so made were able to make medicine that cured many ailments and Civil engineers focused on building and so were able to construct entire cities. Specialization helps us move forward.