Nelson Mandela, who is 75 today, spent 27 years in prison, but he is an exception to the French philosopher's rule.
The president of the African National Congress also defies conventional wisdom on the decaying effects of age, as Elizabeth Taylor, Michael Jackson, Bill Clinton and numerous other luminaries, who queued to meet him on his two-week tour of the US this month, would testify.
ANC officials back in Johannesburg were less concerned about his health than that he might commit another of his celebrated gaffes. Such as meeting, and publicly embracing, Muammar Gaddafi, then causing a stir in Washington by proclaiming from Tripoli that the two men indicted for the Lockerbie bombing should not be handed over to the US for trial. Or praising Fidel Castro on US soil; or speaking on British television of his support for the IRA's 'struggle against colonialism'.
And yet, when he delivered an address at Westminster in May this year - at the invitation of both the Conservative and Labour parties - nearly 300 MPs and peers left the gathering uttering high praise. Why is it that, as a Philadelphia newspaper said two weeks ago, he remains 'the world's last authentic hero'?
In prison it was easy. He was the living symbol of resistance to the one political system in the world that every country, even at the height of the Cold War, agreed to be a crime against humanity. The test came on 12 February 1990, on the morning after his release, when he addressed his first press conference.
If there was a quality that shone through there, it was his generosity. Fresh from prison, almost his first concern was to reassure white South Africans that one person, one vote would not lead to apartheid in reverse.
Beyond words, he conveyed a unique mood, something that prompted the 300 reporters present at the end to break all the professional rules and burst into applause. It is a mood he still conjures up today. He transmits not the slightest doubt about his own importance and power, about the central nature of his role on the political stage.
An EC diplomat said last week that what all his colleagues remarked upon after private meetings with Mandela was his gravitas, his humanity, his charm, his clarity of thought: 'His nearest historical equivalent is Mahatma Gandhi. He is not always sure-footed politically, but he stands somewhere between earth and heaven, beyond the criteria reserved for mainline politicians.'
Most remarkable is the sincerity of his desire to reach out to his erstwhile tormentors and create the non-racial, colour-blind, non- tribal South Africa to which the ANC is committed. Evidence of this is his acceptance of a compromise brokered with the Pretoria government to defer majority rule until the end of the century in favour, after next year's anticipated elections, of a power-sharing government of national unity.
In an address to the nation broadcast live on national television on 13 April, three days after the assassination of the prominent ANC leader Chris Hani - a time when the anger in the black community prompted fears that the country might descend into racial war - he resisted the temptation to cry havoc and let slip the dogs of war. Instead, he highlighted the courage of the white woman, an Afrikaner, who passed on the licence plate number of the suspected killer to the police, and used her example to make a passionate call for peace.
'Tonight I am reaching out to every single South African, black and white, from the very depths of my being . . . Our decisions and actions will determine whether we use our pain, our grief and our outrage to move forward to what is the only lasting solution for our country - an elected government of the people, by the people and for the people.'
It was the speech of a de facto president - barring a disaster, it will be de jure by the time he reaches his 76th birthday - and it made some impact on the white population. Since Mr Hani's assassination, as an opinion poll last week showed, Mr Mandela's support among whites has risen from 1 per cent to 3 per cent. Among blacks it has risen from 65 to 70 per cent. If the white electorate is unlikely in the April election to vote for the ANC in any higher numbers, it is largely because of its conditioning, but partly because it recognises that Mr Mandela will accommodate whites only up to a point.
Unlike the Inkatha leader, Mangosuthu Buthelezi, whose support among whites in the poll was revealed to be 25 per cent (4 per cent among blacks), he is not offering the assurance that the status quo will remain largely untouched after the elections.
Described by an admiring Communist Party stalwart in the ANC as 'a militant old bugger', he lives up to P W Botha's dictum that 'a leader should not be a jellyfish'. At ANC policy meetings, no one is more obdurate when a choice has to be made between honour and compromise. Towards President F W de Klerk he has been as conciliatory as he has been intemperate. After the massacre of 42 ANC sympathisers in Boipatong township last year, Mr Mandela described Mr de Klerk as a murderer, declaring that the ruling National Party, the police and Inkatha were killing people simply because they were black.
Mr Mandela succumbs easily to his emotions, and outbursts of this kind have often served the useful political purpose of binding the ANC leadership and its supporters at times when the latter, drowning in blood, have doubted the validity of persisting in talks with the government. Vociferous among these has been his estranged wife, Winnie, who has railed against the ANC leadership's 'unseemly haste' to wrap itself in 'the silken sheets' of office. It was thought at the time of the marital separation in April last year that Mr Mandela, his eyes painfully opened to his wife's crimes and infidelities, might crack under the strain. He has not, and besides, unlike Mrs Mandela, has had the moral courage to offer a gesture of contrition to the mother of Stompie Moeketsi Seipei, the 14-year-old boy kidnapped by Mrs Mandela and murdered by a member of her 'football club' of bodyguards.
On Thursday last week he addressed a rally at her home town of Parys and, having insisted she be given a place of honour on the podium, he spoke to her at length, pointedly, for all to see. She declared herself delighted afterwards, as did Sergeant Henk Prinsloo after Mr Mandela dropped in unexpectedly at the local police station. No institution has inflicted more suffering on the black population in general and Mr Mandela in particular than the South African police. But he told the local force that the time had come to forget the mistakes of the past and transform the police into 'South Africa's pride'. Asked by Sgt Prinsloo to sign the visitor's book, Mr Mandela wrote down, in Afrikaans, what people the world over will be saying to him today: 'Compliments and best wishes.'