“As it is far better to excel in any single art, than to arrive only at a mediocrity in several; so on the other hand, a moderate skill in several is to be preferred, where one cannot attain to excellency in any.”
Ut satius unum aliquid insigniter facere quam plura mediocriter, ita plurima mediocriter, si non possis unum aliquid insigniter.
Letter 29, 1.
Letters, Book IX