A warning to those who are too introspective (4,3)
I believe the answer is:
look out
If this is the answer, I'm afraid I cannot explain it.
Can you help me to learn more?
(Other definitions for look out that I've seen before include "as Wenceslas did" , "Be on your guard!" , "Be watchful" , "Take care" , "A view of the future" .)