A man always is to be himself the judge how much of his mind he will show to other men
 Thomas Carlyle, On Heroes, Hero-Worship, and The Heroic in History (1841). copy citation

Context

“Such a man must have reticences in him. If he walk wearing his heart upon his sleeve for daws to peck at, his journey will not extend far! There is no use for any man's taking up his abode in a house built of glass. A man always is to be himself the judge how much of his mind he will show to other men; even to those he would have work along with him. There are impertinent inquiries made: your rule is, to leave the inquirer uninformed on that matter; not, if you can help it, misinformed, but precisely as dark as he was!” source