Seneca the Younger, Epistulae, V.45.1:
Librorum istic inopiam esse quereris. Non refert quam multos sed quam bonos habeas: lectio certa prodest, uaria delectat. Qui quo destinauit peruenire uult unam sequatur uiam, non per multas uagetur: non ire istuc sed errare est.
You complain that there are not many books where you are. It is not the quantity of books in your possession but their quality that matters: circumscribed reading has its uses, desultory reading is merely for amusement. One who has settled on going somewhere should follow a single path and not wander about aimlessly: that is the not going somewhere but wandering aimlessly.
My translation.