How much difference can one leader make?

It's easy to forget, nearly 20 years on, how deep were the fears in 1994 as South Africa prepared for its first, genuinely free, multi-racial elections.

In just the few weeks before the poll, weapons were reported stolen from an air force base; 21 prisoners were killed in a jail riot; 30 people were killed during violent protests by Zulus in Johannesburg; a state of emergency was declared in Kwa-Zulu Natal; and nine people were killed and more than 90 injured when a car bomb exploded in central Johannesburg.

Wherever you went -- and I was there at the time -- there were predictions of a bloodbath to come. The white minority would launch a coup; the armed forces would mutiny; tribal tensions would explode into an orgy of violence and killing.

None of it happened. And for decades to come, earnest historians will earnestly debate why not. Was it all because of one man: Nelson Mandela?

If there had been no Mandela, or if Mandela had been a different kind of man, would South Africa's destiny have been different? How much difference can one man make?

These are not, I know, original questions. But I think, for obvious reasons that I don't have to spell out, this may be a good weekend to ponder them.

What about Gandhi and India? Hitler and Europe? Abraham Lincoln and the United States? King Henry VIII? Winston Churchill? Mikhail Gorbachov? There's a long list of leaders of whom many would say they changed the course of history.

Look at those names again: what, if anything, do these leaders have in common? Perhaps at its most basic, it's simply a self-belief so strong that when everyone around them was saying "You can't do that", these men replied: "Oh yes, I can."

How many people must have told Gandhi that a campaign of non-violence would never force Britain to leave India? How many people told Churchill that his determination to win at all costs against Nazi Germany was doomed to fail? And how many people told Mandela that reaching out to South Africa's whites with a message of reconciliation was naïve and dangerous?

I'm not a great fan of "What if …?" questions -- but I've always been intrigued by the relationship between the individual and the sweep of history. We all have our faults, even the greatest of leaders -- perhaps especially the greatest of leaders -- and when the time comes to draw up the balance sheet, it is right that there should always be two columns, one for the pluses, and another for the minuses.

Euripedes, writing nearly 2,500 years ago, clearly wasn't thinking of tyrannical rulers when he said: "When good men die their goodness does not perish, but lives though they are gone. As for the bad, all that was theirs dies and is buried with them."

The bad that was Hitler's, Stalin's, or Pol Pot's, did not die with them -- the consequences of their pernicious evil lives on to this day and can be seen and felt far and wide.

But similarly, so too can the good that was done by leaders like Mandela. Heaven knows, South Africa has no shortage of problems -- and you will soon be able to read dozens of pieces along the lines of  "Whatever happened to Mandela's dream?"

Yes, of course, South Africa could, and should, be so much better than it is. But it also could have been so much worse. And for that, I suspect, we do have one man to thank.