Vom wahren Gegner fährt grenzenloser Mut in dich.
From the true antagonist illimitable courage is transmitted to you. [Kaiser/Wilkins]
From the true opponant, a limitless courage flows into you. [Hofmann]
Your opponant must also derive comparable courage from you. What matters is that the opposition be true. A false opposition gives no courage because there is nothing to overcome. Where the opposition is true, the courage is limitless, perhaps because true opposition is limitless. It may take limited forms, or run its course in time, but the opposition of directions is strict.
This means that you -- and again Kafka uses the informal dich, possibly addressing himself -- generate your opponant by adopting a contrary position. Josef K. insists that the Court is his adversary, even in the absence of any hostilities.
I am only defeated where there is no fight, even though the struggle is an impasse. The impasse is a kind of success, because victory, which abruptly clears away all signs of struggle, is indiscernible in this respect from defeat or from there never having been any struggle.