It is better, of course, to know useless things than to know nothing. Seneca
If you see a man who has sinned and you do not pity him, the grace of God will leave you. Whoever curses bad people, and does not pray for them, will never come to know the grace of God. Silouan the Athonite
To know your Enemy, you must become your Enemy. Sun Tzu
Not to know is bad; not to wish to know is worse. Nigerian Proverb
All things good to know are difficult to learn. Greek Proverb
Not to know is bad, not to wish to know is worse. African Proverb