Though Fail-Safe is a novel anchored, so to speak, in its own time—the early 1960s and the Cold War era—its themes are relevant today because the underlying issues with which they deal are still with us. First, one of the principal messages of the book seems to be that, regardless of the "safeguards" built into an automated system, a potentially disastrous error can and will occur. At the time Fail-Safe was written, computers were a relatively recent invention and were thought of by the general public as awesome machines which could run amok and "take over." But the theme that underlies this aspect of the novel is that it's man who has created the automated systems and that man and his own weaknesses are the real danger.
This point leads to another theme that may be even more significant: the moral responsibility of a leader, and the question of right or wrong in any conflict. When it is revealed that a nuclear attack against the Soviets has inadvertently been ordered, the civilian advisor Dr. Grotoschele recommends that nothing should be done to stop it—that faced with destruction, the Soviets will back down, surrender, and the threat of communism will be ended. The president rejects Grotoschele's suggestion, but the authors are posing the question of whether war is "moral" in certain situations in order to "prevent" war. This, in effect, was the reasoning behind the nuclear attack on Japan in 1945—that by dropping atomic bombs on Hiroshima and Nagasaki, the US would end the war quickly and thus avert a greater number of deaths that would have occurred had combat continued.
In summary, Fail-Safe expresses themes about man's vulnerability and the danger to himself created by his own imperfections. It also raises the question of whether any action under certain circumstances can be regarded as "moral" or justified, and whether a "right" or "wrong" exists in a conflict. In the story, when the president speaks on the hot-line with the Soviet premier, we get the sense that both men, despite their ideological differences, are just human beings struggling with the same problem. Thus, a final theme of the novel is the commonality and basic unity of human beings in crisis.