A rich, and pointed, passage by Sertillanges on the intellectual’s need to be solitary but not isolated:

[Do] not forget that in association with others, even in ordinary everyday meetings, there is something to be gleaned. Too much solitude would impoverish you. … [You] must feel that you cannot shut yourself up entirely. Monks themselves do not do it. You must keep, in view of your work, the sense of the common soul, of life, and how could you have it if, cutting yourself off from human beings, you had in mind but a dream-humanity? The man who is too isolated grows timid, abstracted, a little odd: he stumbles along amid realities like a sailor who has just come off his ship; he has lost the sense of the human lot; he seems to look upon you as if you were a “proposition” to be inserted in a syllogism, or an example to be put down in a notebook. In the inexhaustible wealth of the real, too, we can find much to learn; we must move in it in a spirit of contemplation, not keep away from it.

— A. G. Sertillanges, The Intellectual Life: Its Spirit, Condtitions, Methods, 59. “The inexhaustible wealth of the real”: what a marvelous phrase.