Institutio Oratoria

It is generally and not unreasonably regarded as the sign of a good teacher that he should be able to differentiate between the abilities of his respective pupils and to know their natural bent. The gifts of nature are infinite in their variety, and mind differs from mind almost as much as body from body.

This is clear from a consideration of the orators themselves, who differ in style to such an extent that no one is like another, in spite of the fact that numbers have modelled their style on that of their favorite authors.