The teacher often says 'learning without thought is confusion', and asks us to keep asking why.
Tips
history
From the Analects 《论语·为政》: 子曰:学而不思则罔,思而不学则殆 — 'The Master said: to learn without reflecting is to be lost; to reflect without learning is to be in danger.' Confucius here names the two failure modes of the mind. The two halves are always cited together in educational discourse.
usage
Paired couplet — typically spoken or cited with its mate 思而不学则殆. Classical register; standard in teaching, essays, and self-discipline talk. 罔 here is a classical reading meaning 'confused / deluded', not the modern 'net' sense.