Most of us value “the ideal of a democratic and free society in which all persons live together in harmony and with equal opportunities.” But how many of us could stand up and say in complete honesty that “if needs be, it is an ideal for which I am prepared to die”? That is what Nelson Mandela declared on 20 April 1964 at the trial that led to his imprisonment, and there is every reason to believe him.

In comfortable, affluent democratic societies, self-sacrifice for a higher good can generate both admiration and bewilderment. For much of human history, people have grown up among people who have died to protect their societies, or who remember those who did. That one might be called to do the same was just a fact of life. To refuse to do so would have led to ostracisation at best, death by some other means at worst. Recent remembrances of the Great War of 1914-18 have tended to gloss over the extent to which those who died in the trenches faced little choice. 306 soldiers were shot for cowardice or desertion and they were only finally pardoned in 2006. The tarring and feathering of men who didn’t go off to fight also persisted until the early twentieth century, with other forms of humiliation and blackballing common.

Risking our own lives has also become more fearful because we have so much more to lose. Before the advent of modern medicine, the sense that anyone was just one infection away from death would have been very strong. We remain acutely vulnerable but with life expectancy longer and more and more diseases treatable, an early grave is no longer considered a natural risk but a kind of abomination, ridding us of our right to long life and prosperity.

Put these two factors together and the idea of willingly facing death, not in simple self-defence, but in the name of an ideal, looks both courageous and reckless. Military heroes, for example, are praised by people who would never dream of going to war and, if they were honest, think anyone who would do so voluntarily is a little bit mad.

Nelson Mandela was clearly not crazy. In fact, he is probably the most admired individual in twentieth century history. We can understand why he chose to risk his life because of the brutality and manifest of injustice of apartheid. It’s not difficult to see why some would rather die on their feet than live on their knees, as Zapata famously put it. But still, there were millions of oppressed people in South Africa and most of them did not put their own necks on the line. What is it that makes some do so?

Answers to such questions always involve some aspect of personal psychology. Some people love risk and danger, others have Messiah complexes, some are driven by ideological fervour. Listen to Mandela’s speeches, however, and none of these factors seem relevant to him. He makes a case for the justice of his cause which is calm, rational, unanswerable. His fellow black South Africans would have cheered every word, but grateful that Mandela, not they, were in the dock uttering them.

I think we all know what it is like to feel the moral force of an argument but to be unwilling to take inconvenient action on the basis of it. For example, I know of people who claim to be 100% convinced by the moral case for vegetarianism but who say they just can’t bring themselves to stop eating meat. Many philosophers have argued that this is incoherent, that to believe something is right is to be motivated to act accordingly. These philosophers are not very good psychologists. For them weakness of will is a paradox, a desire to both do and not do something at the same time. For the rest of us, it is the human condition and all-too understandable.

I don’t suspect that people like Mandela were moved to act on the basis of a moral argument. Rather, I think that often people are called to what we term “self-sacrifice” precisely because they think that not acting sacrifices an even greater self, or part of themselves.

Listen to the opening paragraph of Mandela’s speech. He starts by talking not of justice or of morality but of his people in the Transkei, the elders of his tribe telling stories “of wars fought by our ancestors in defence of the fatherland”.

“I hoped then that life might offer me the opportunity to serve my people and make my own humble contribution to their freedom struggle,” he said. “This is what has motivated me in all that I have done.”

Mandela was not risking his life primarily for an abstract cause or principle. He risked it for his people. His individual life was worth risking because he never existed as a pure individual, only as a member of that people. He did not experience the injustices of apartheid as merely personal violations against him but as violations against the whole of society. He stood up for others because it was because of others that he was able to stand up at all.

This is where the language of self-sacrifice becomes potentially misleading, in that it risks giving an impression that the self in question is making a sacrifice for something completely other than his or herself, rather than for something of which he or she is a part. This mistake is natural in individualistic cultures. The philosopher Tom Kasulis observes that when people are called to risk their lives in these societies, they are called to defend the values that “bind us together”. This image suggests without something external to us do do the binding, we are simply a collection of individuals. In such a society, any scarifice of self-interest is called altruism, literally meaning regard for others.

However, in less individualistic cultures, which includes traditional South African society, such actions are not other-regarding at all because it makes no sense to think of the whole as separate from its parts: individual selves. The exhortation to fight for the common good asks us “not to go outside the self but to look deeper within,” says Kasulis. When Mandela fought for his people he was of course also fighting for himself, because his own self cannot be separated from his people.

There is another sense in which what we call self-sacrifice is in fact a refusal to sacrifice our selves. Paul Rusesabagina was a hotel manager in Kigali when the Rwandan genocide broke out. He risked his life to protected 1,268 Hutu and Tutsi refugees from the interahamwe militia. Explaining his decision in his memoir, he said “If I left, they would be killed, and I would never be a free man”. Sometimes, our beliefs, our values are so integral to our identity that to save our skins at their cost would be to give up too much of who we are. That would be a kind of sacrifice of self that many find worse than the prospect of death.

That is why people like Rusesabagina and Mandela do not feel like heroes, even as other laud them. What they do they feel they must do. That does not make their actions any less admirable. If anything it makes them more so. They understand better than most of us that people are not individual atoms but exist only in relation to others. And their values are embedded more deeply than most, not just fine words they pay lip service to, but moral imperatives that have a claim on them.

Those of us who find it hard to imagine how and why people can risk their lives for others should consider that we are the strange ones, not them. The modern individual has become so detached, so autonomous as to think that even moral choices can and should be picked and chosen, like cereals off a supermarket shelf. The idea that morality has a claim on us threatens our sense of autonomy. We protect our own lives so much because they have become like little glass beads, self-contained and hard to penetrate. Self-sacrifice is harder to make or understand when the self is so small and vulnerable.

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Julian Baggini is a philosopher and writer, who is also currently the editor of The Philosophers' Magazine, a publication he co-founded in 1997.

He gained his PhD in the philosophy of personal identity from University College London. Julian is the author of several books, including a number of academic textbooks and has written for a variety of newspapers including The Guardian. He is a regular guest on BBC radio, and has also made numerous appearances on TV.