Someone once said doubt is the tax that man pays for knowledge - and the taxman began to knock more insistently on the door of my certainty about Conrad Smith in the All Black centres during the last test against the Springboks.
I know, I know ... it's only one game and the 33-year-old Smith is the maestro of the midfield. But Bok centres Damien de Allende and Jesse Kriel had the better of Smith and Ma'a Nonu while both were still on the field last weekend. The younger, more powerful de Allende, in particular, asked questions of the All Blacks that weren't entirely answered.
Let's be clear - Smith will be the starting centre for the All Blacks at the World Cup. But once doubt wriggles its way into your brain, it invites its best mates (uncertainty and indecision) in for a debate.
Coach Steve Hansen and his lieutenants have managed things so well thus far they have largely dispatched the fears of all those unbelievers who felt - and some still feel - that the All Blacks are putting too much store in experience over the energy and game-breaking brilliance of the younger brigade. To an extent, those fears were played up in the first half against the Boks when de Allende and Kriel were doing their thing.
Let's think back to when Richie McCaw's form was being fiercely criticised by the dropkicks who simply could not see he was being brought up the curve slowly, to peak at World Cup time. They're all quiet now, those people, aren't they?
Watch the replay of last weekend's test and marvel again at McCaw's effectiveness and industriousness - and I'm not talking about the try from the lineout. He was up against a canny selection and crafty opponent in Heinrich Brussow but McCaw was simply outstanding.
Dan Carter hasn't yet reached the same level as McCaw in this build-up but he, too, is clearly on the way. Bringing him to the boil slowly is so obviously the best way to take into account age and injury that you wonder about the insight of those who also called for Carter to be led into the home paddock to wait for the meat truck.
No one in their right mind would go into a World Cup without the savvy of those two players. So the same argument would apply to Smith, right? After all, Smith's worth is also weighed in some of the highly valuable intangibles that add up to the All Blacks winning test matches, like last week's, when perhaps they shouldn't:
* Composure under intense pressure - check
* The ability not just to make linebreaks but to put team-mates in position to do so - check
* Distribution/judgement of a pass; the property of great All Blacks centres like Robertson, Stanley, Bunce, Little (Paul), Davis, Umaga and another Smith (J.B.) - check
* Rugby smarts; the instinct to know where ball/man/dummy runner/kick is going - check
* Leadership, marshalling the backline defence; a cool head in one of the hottest spots on the field - check
So it's a no-brainer. Well, all except for one small thing: pace.
Last year Smith was embarrassed by England winger Jonny May who simply ran around him to score. The All Blacks got their defence wrong on that occasion - Smith should not be looking after a winger - but May made him look slow. May himself has done little since and is struggling to make England's World Cup squad.
Then look at the advances Kriel and de Allende made through the All Black midfield. Some of that was power but you wondered a time or two whether Smith's legs were getting him to the right place in time. Pace is not the be-all and end-all for a centre but it is undeniably handy. It can help cover mistakes and misjudgements.
Springboks coach Heyneke Meyer said later fewer than 20 per cent of his squad had hit their fitness marks before the Rugby Championship - suggesting the Boks are also building up to a peak and helping to explain their lacklustre finish to their last two test matches. They have their own youth v experience challenges - do they slot skipper Jean de Villiers back into the midfield after his long injury lay-off or do they turn to de Allende and Kriel? Not to mention 38-year-old lock Victor Matfield. Their case for youth looks more compelling - if the Boks are to win the World Cup, they may need new, relatively unseen talent.
Bottom line: if I was Steve Hansen, I'd stick with Smith. Malaki Fekitoa looks a better prospect from the bench right now. Charlie Ngatai, though he seems to have been around for yonks, is only 24 and still developing. He has nascent Smith qualities with Fekitoa more Nonu in style.
Smith's foray against the Wallabies on Saturday will be interesting but maybe not conclusive. The Australians do not have as powerful a midfield as the Boks, although Tevita Kuridrani can be a handful.
And that's the tough thing about World Cup year - doubt creeps in like rising damp. Certainty moves from being a comfort to a conundrum.