“A man can be himself only so long as he is alone; and if he does not love solitude, he will not love freedom; for it is only when he is alone that he is really free.”
Schopenhauer links solitude with freedom from the constant accommodation that social life requires, especially for strongly individual temperaments.
Source details
Counsels and Maxims, chapter on our relation to others, translated by T. Bailey Saunders.