If you know the enemy and you know yourself, you will win every battle that you fight

“If you know the enemy and you know yourself, you will win every battle that you fight” is the strategic principle Director Zheng uses to distinguish Rong Jinzhen’s cryptographic work from the more conspicuous achievement of building a nuclear weapon. In the novel, the expression names intelligence as a form of access to an opponent’s hidden intentions, while the difficult work of gaining that access exposes how uncertain and costly such knowledge can be.

Zheng’s strategic argument

In a telephone interview, Director Zheng reacts angrily when the interviewer says that people at the university imagine Rong played a key role in building the country’s first nuclear bomb. He rejects that attribution, but not because he considers Rong’s service minor. The nuclear programme, he argues, displayed national strength; Rong’s work served a more directly practical military purpose by helping the country understand other people and their secrets. He invokes the expression to make that distinction: victory depends not only on possessing force, but on knowing the adversary and oneself.

The contrast gives the saying a particular weight. Rong is an unknown hero because his work is secret, yet that secrecy also encourages inflated claims about what he did. Director Zheng’s correction redirects attention from the imagined role in the nuclear programme to the actual significance of cryptography. The expression is therefore not a general assurance of victory. It is Director Zheng’s explanation of why deciphering an opponent’s communications could matter more in practice than a public symbol of power.

Knowledge and the labor of cryptography

The novel sets that strategic ideal against the ordinary method of codebreaking. Intelligence agents gather relevant information; cryptographers use it to develop hypotheses and test possible solutions. Director Zheng describes the process as designing keys and doors, then trying them against an immense range of possibilities. The labor depends both on how much material is available and on the cryptographer’s sensitivity to the particular cipher. Though he calls this method simple and unsophisticated, he also describes it as the safest, most secure, and most effective approach, especially for high-level ciphers.

Rong does not confine himself to that cautious route. He studies the history of cryptography, entering territory that Director Zheng treats as forbidden because the field’s practitioners cannot safely build on the work of their predecessors. Its history is portrayed as lonely: cryptographers face closed doors and traps, often forced onto side paths rather than an open road. The historical approach might narrow the search—for instance, by eliminating half of 10,000 possible byways—but its limited reduction does not guarantee success. The expression’s promise of mastery thus meets a discipline in which even an informed advance can leave the crucial possibilities untouched.

Errors, silence, and countermeasures

The account makes the adversary’s behavior part of the cipher. A code may appear seamless, but its use can produce errors that reveal a point of entry. A cryptographer must wait for such a slip and recognize its significance. Director Zheng describes Rong’s work as a long exercise in patience: through countless days and nights, Rong waited for an opening in BLACK, but found no detectable error and could not decipher it.

Unit 701 considers two explanations for this failure. First, cracking PURPLE had made the adversary more cautious, encouraging deliberate handling of communications and reducing the chance of another revealing mistake. That success had made Unit 701 feel invulnerable, but it may also have changed the conditions of the next contest. Second, Liseiwicz understood Rong’s abilities well enough that he could have warned the creators of BLACK and helped them devise countermeasures. The two men had once been close, but political positions and beliefs had opened a profound spiritual distance between them. When Unit 701 learned that Liseiwicz was Weinacht, its members wanted to warn Rong about the deception. Rong’s response, “Tell him to go to hell, this devil in the temple of science!”, shows that personal anger complicated the practical demand to know the enemy.

The zero key and the limit of the maxim

The eventual solution to BLACK arrives not through an ordinary search among keys but through a startling absence of a real lock. At three in the morning, after pacing alone in his office, the narrator takes out a calculator capable of more than 40,000 calculations to test his assumption. Once he has deciphered BLACK, he rushes out of the underground office in the mountain cave, falls to the ground, and cries out before dawn. The key, he explains, was in a leather attaché case; it was the number zero.

The discovery makes the maxim’s promise more complicated. Knowledge of an enemy remains essential, but the decisive opening may not resemble a key at all: BLACK seemed firmly secured while presenting only a false façade, and the door swung open when pushed. The narrator insists that he could not manufacture keys and therefore did not experience the result as the triumph of a deliberate search. The expression’s ideal of knowing both sides illuminates the purpose of cryptography, while BLACK’s solution underscores how that knowledge can depend on an unforeseen opening as much as on patience, skill, or force.