According to my experience and judgment, I can learn calligraphy well without the guidance of a teacher. The speed of progress is related to your writing foundation, understanding, talent and interest. The important thing is persistence. If we can find a "master" instead of a "famous teacher" for guidance, the progress will be faster and the effect will be more obvious.
Remarks: When I say "Master", I mean a teacher who understands the truth and can give you correct guidance. A "famous teacher" refers to a famous teacher whose handwriting is not good, unreasonable or even misleading. Therefore, "a master should not be a famous teacher".