This changing line answers a querent facing an obstruction that will not yield to ordinary effort, and its counsel is unusually procedural. Before pressing on, state honestly how hard the thing actually is. The text makes advantage conditional on exactly that recognition, and the reason is practical rather than moral: a task undertaken with the wrong estimate of its size gets abandoned partway, at the worst possible moment, when the cost has been paid and the reward has not yet been reached.
What the line promises in return is solid. Metal and arrows are pledges that hold their shape, so the outcome of persistence here is a durable commitment, a settled agreement, or a resolution that will not need reopening. Readings landing on this line often concern negotiations that have gone on too long, entrenched institutional problems, or a relationship difficulty that everyone has been working around rather than through.
The stroke is yang in an even place at the base of the upper trigram Li, firmness where yielding is formally expected, which is where the risk lives. A querent with real force available may be tempted to apply all of it at once and break what should have been separated patiently. Firmness in this line means duration rather than intensity. Sustained pressure with a clear view of the difficulty produces the good fortune promised; a single hard push, made without measuring the task, produces the wasted effort the line is written to prevent.