Crossing into the upper trigram, Modesty repeats its instruction instead of advancing it. Legge's translation says of the fourth line that nothing its subject does will fail to be advantageous, and that what is called for is stirring up humility all the more. No new virtue is introduced, no reward is named, and the absence of both is the character of the position. The line describes a state in which action is safe precisely because the person acting keeps deepening the one quality that makes them safe.
A yielding stroke stands in an even place, correctly positioned, at the base of the upper trigram Kun, the earth. Two pressures meet here. Directly below sits the hexagram's single strong line, with real merit behind it; directly above sits the ruler. A minister between an able subordinate and a sovereign is the classical picture of a position that could easily go wrong, either by claiming the achievement below as its own or by crowding the authority above.
The line's answer to both risks is the same, and it is why the instruction is to increase humility rather than to balance interests. Someone who presses no claim in either direction has nothing to be resented for in either direction, and that is the whole content of the promise that nothing will be unfavorable. It is not a prediction of success. It is a statement that a person in this position who stays out of the way cannot be harmed by it.