If you ever want to be reminded of the fine line Kevin Pietersen runs between the spirit and the talent of the very greatest cricketers on one hand, and Coco the Clown on the other, you simply must return to the first Test which ended so perilously for England here last evening.
It is mandatory because probably nothing will ever quite so perfectly illuminate the split personality of a man who turned a day that was supposed to be about desperate survival into an exhibition of how a sportsman of genius can utterly dominate all around him.
Then, literally, ran out of the most basic common sense.
Nineteen runs short of his 17th Test century, the South Africans, who walked out in the sunlit morning so buoyantly, wilting under the sheer weight of his ability to play sublime shots, Pietersen went for a quick single that in the context of the game could hardly have been more gratuitous.
It is true that it was his call, and that his team-mate Jonathan Trott was maybe at fault for not backing up or responding at all purposefully to the command of the much more experienced Pietersen. But Trott did shout "no", which no doubt partly explained his hard-nosed refusal to surrender his wicket.
Also of significance is that Trott, who made a century on his Ashes debut at The Oval, was playing in a Test match for the first time with his fellow South African-born team-mate and nothing that had happened in the previous two hours, when they had built together England's survival with a fine mixture of patience and rich stroke-play, could have prepared him for Pietersen's rush of strange blood.
It would have been a rash call in some two-and-a-half-penny Twenty20 game. In the opening Test match of a series of four which simply had to be saved it was, well, beyond reason and, to be fair to the bemused and saddened Trott, any reasonable anticipation.
The potentially disastrous consequences of Trott, Ian Bell, Matt Prior and Stuart Broad trailing back to the dressing room in Pietersen's wake could only underline the extent of the brilliant batsman's folly – and bring fresh incredulity to the belief of English cricket's rulers that he was a suitable candidate for the captaincy.
Now, certainly, he was the most forlorn of figures as he looked out from the dressing room on to a field of long shadows where, with just four overs left, Graeme Swann, a first-innings hero with 85 runs, became another victim of the late assault led by Test debutant Friedel de Wet, Morne Morkel and spinner Paul Harris.
De Wet has a little Bambi hop early in his run-up but if England doubted it before, they knew now that they were being confronted by a 29-year-old with a heart equal to the challenge that had been so long coming.
As De Wet bowled his way to four wickets and what so easily might have been an indelible place in South African cricket history you could only speculate on the depths of Pietersen's despair. He nibbled at his finger-nails, he looked as though he was replaying all the points of pressure that had come in a dispiriting year.
First, there was that shattering loss of the England captaincy.
In the summer, he hobbled out of the Ashes series – but not before provoking fresh questions about the maturity of his handling of superb gifts. At the first Test in Cardiff, he batted with impressive restraint – as he did here yesterday while mixing in some beautifully timed and shaped shots – but then left because of a shot of bewildering laxity. This last week the challenge was to prove that he had recovered both his fitness after a severe Achilles tendon injury and the competitive nerve that gave him the fastest growing reputation in world cricket and made him the most expensive performer in the Indian Premier League.
It hardly helped when South African captain Graeme Smith promised the most hostile reception for the man who left his homeland complaining about the positive discrimination that was applied to team selection.
Smith said, "I want this to be a major test for Kevin. Yes, we have prepared a special game-plan for him."
With Pietersen stroking the ball so exquisitely yesterday on his way to 81, you had to conclude that Smith might as easily have tried to wrap his hand around a gust of wind.
Not only did Smith fail to staunch the flow of Pietersen's game, he also suffered the disturbing thought that at the rate of scoring achieved before the run-out, England might have first ensured survival, then launched a late assault on the winning target of 356 they faced when they went out to play a last-day innings without the bulwark of captain Andrew Strauss, dismissed at the end of Saturday's action.
Had that happened, had England achieved one of their most unlikely victories, rather than survive by one wicket through the typical defiance of Paul Collingwood and the last-over heroics of Graham Onions, there is no doubt where the greatest debt would have rested.
It would have been with Pietersen, a tragi-comic villain in the end but one who had earlier lifted England from the vast pool of his natural gifts. When he joined Trott, England had slumped to 27 for three. When he left, booed with great derision by his former compatriots as he waited for Collingwood to complete his walk from the dressing room, England were 172 for four.
Pietersen had made a brilliant, calm alliance with Trott and when they were in their richest vein, dispatching the legendary but waning Makhaya Ntini for 13 runs in one over, it seemed that anything was possible. But then with Pietersen, one way or another, it generally is.
Recently he declared: "I'm putting all the malarkey behind me." Presumably, he meant the bling and the blonde streaks in his dark hair and the relentless pursuit of growing celebrity. However, jewellery and bleach are not so hard to discard; at least when compared to a nagging flaw in the nature of a great sportsman. It means that England may have to accept that they must always value the best of Kevin Pietersen – and try to survive the rest.