I came across this on Farnam Street, and it really resonated. Seneca said (emphasis mine):

The primary indication, to my thinking, of a well-ordered mind is a man’s ability to remain in one place and linger in his own company. Be careful, however, lest this reading of many authors and books of every sort may tend to make you discursive and unsteady. You must linger among a limited number of master-thinkers, and digest their works, if you would derive ideas which shall win firm hold in your mind. Everywhere means nowhere. When a person spends all his time in foreign travel, he ends by having many acquaintances, but no friends. And the same thing must hold true of men who seek intimate acquaintance with no single author, but visit them all in a hasty and hurried manner. Food does no good and is not assimilated into the body if it leaves the stomach as soon as it is eaten; nothing hinders a cure so much as frequent change of medicine; no wound will heal when one salve is tried after another; a plant which is often moved can never grow strong. There is nothing so efficacious that it can be helpful while it is being shifted about. And in reading of many books is distraction.