Six mooring lines and what each one is for
A boat on six lines is not over-secured, it is correctly secured. The bow and stern lines stop it drifting off. The springs, running fore and aft along the hull, stop it surging up and down the berth as wakes come through, and they are the lines that do the real work in a busy harbour. The breast lines hold it close alongside for loading and come off again before you leave. Confusing a spring for a breast is the most common reason a well-tied boat still chafes.