瞻 (zhān): To look ahead; to gaze into the distance. It implies a more formal and focused looking than the common character 看 (kàn).
前 (qián): Front; forward; ahead.
顾 (gù): To look back; to turn one's head to look; to consider or take into account.
后 (hòu): Back; behind; rear.
These characters combine literally and powerfully to mean “gaze forward, consider behind.” The idiom paints a vivid picture of a person who is physically and mentally checking their surroundings and all possibilities before proceeding.