Donald Rumsfeld – remember him? – might have put it this way. When it comes to Cardiff Blues, there are known knowns, and known unknowns.
The facts that Martyn Williams is a wonderful open-side flanker, and that Xavier Rush is among the two or three best overseas recruits of the decade, fall into the first category, while the Welsh region's newly discovered stubborn streak falls into the second. (We've been aware of its existence all season, but not the extent of it). As for the unknown unknowns, we'll find out about those over the next three weeks.
A year ago, the Blues could not have won this quarter-final, although they would have given it their best shot. Two years ago, they might have lost by 30 points and considered themselves lucky. Few teams possess the heart and soul to withstand Toulouse when the Frenchmen arm themselves with the full arsenal of attacking weaponry, and while there was a frustrating lack of accuracy about the visitors on Saturday, no one could argue that Maxime Médard, Vincent Clerc, Yannick Jauzion, Byron Kelleher and Thierry Dusautoir failed to fire all the bullets available to them.
Yet when the serious questions were asked, the Blues found the answers somewhere, somehow. Leigh Halfpenny, their eye-catching little wing, made two tackles in the last quarter that will live in the memory: the first on Yannick Nyanga as Europe's fastest flanker broke free in open field and threatened to run the length; the second on Clément Poitrenaud, the inside man on a two-on-one overlap.
This last hit, as late as the 77th minute, was a life-saver. Had the ball found its way to Clerc in space, it would have been a case of "thank you and good night". Halfpenny was not alone in manning the barricades. Dear old Jason Spice, deep in his 35th year, was exemplary in this regard; so too was Gethin Jenkins, who would be the best loose-head prop in the game if he enjoyed scrummaging as much as tackling.
As for the New Zealand contingent, there was no questioning their appetite for the fray. Ben Blair, Paul Tito and the tireless Rush have been the core figures in Blues' transformation from wastrels to workaholics. All made mighty contributions in securing their team a first Heineken Cup semi-final in more than a decade.
If Toulouse felt hard done by – they were disappointed by the video official's decision not to award Dusautoir a close-range try midway through the first half, and both the coach Guy Noves and the lock Fabien Pelous muttered something about getting a raw deal from the on-field referee Chris White – they were not of a mind to throw a fit about it.
The depth of their opponents' commitment was not lost on them, and they left the Millennium Stadium with renewed respect for the team they beat in the first Heineken final, way back in 1996. "This defeat had as much to do with their strength as our weakness," acknowledged Pelous, generously.
Things are happening in the Welsh capital, clearly. There was the best part of 37,000 spectators in the ground – "A huge statement of support for rugby in the region," said David Young, the Blues' coach – and with new half-backs signed for next season, there is an onwards-and-upwards feel to the place.
Not that the existing half-backs, both of them bound for the English West Country at the end of term, did too badly here. Spice was a model of determination, even though his kicking game left a little to be desired, while Nicky Robinson made one lovely break from stand-off that might have put things to bed inside an hour.
Robinson's slicing-up of the Toulouse midfield broke the game open, and for the final 20 minutes there was a veritable riot of attacking rugby. It did not, despite what certain people from the International Rugby Board would have you believe, matter a jot that the contest finished try-less, for there was more to savour here than in any 47-39 pantomime you might witness in the southern hemisphere. To true rugby aficionados, or course, this is a known known.
Scorers: Cardiff Blues: Penalties Blair (3). Toulouse: Penalties Michalak, Skrela.
Cardiff Blues: B Blair; L Halfpenny, T Shanklin, J Roberts, T James; N Robinson, J Spice; G Jenkins, G Williams, T Filise (J Yapp, 73), B Davies (D Jones, 59), P Tito (capt), M Molitika (A Powell, 63), M Williams, X Rush.
Toulouse: M Médard; V Clerc, F Fritz (M Kunavore, 59), Y Jauzion, C Heymans (C Poitrenaud, 76); F Michalak (D Skrela, 59), B Kelleher; D Human (Y Montes, 59), W Servat, S Perugini, F Pelous (G Lambole, 68), P Albacete, J Bouilhou (capt, Y Nyanga, 59), T Dusautoir, S Sowerby.
Referee: C White (England).