Nine in the fourth place means

He treads on the tail of the tiger.

Caution and circumspection

Lead ultimately to good fortune.

This text refers to a dangerous enterprise. The inner power to carry it through is there, but this inner power is combined with hesitating caution in one's external attitude. This line contrasts with the preceding line, which is weak within but outwardly presses forward. Here one is sure of ultimate success, which consists in achieving one's purpose, that is, in overcoming danger by going forward.