Among the pleasures to be derived from watching sport is the proving, or disproving, of assumptions.
They can make us all feel just a bit clever, unless we get it wrong.
We've all done it. You form an opinion, based on a range of elements which could include cold logic, form or simple bloody-minded, unshakeable belief in your team, no matter the odds.
You watch the game and see your firmly held convictions either come true or make a goose out of you.
It would be a dull old existence if those assumptions were always proved correct. Mind you, the bank balance would be a fair bit healthier.
And if you think New Zealand rugby fans come from the blinkered side of fair-minded, take a look at images from the English Premier League, as supporters see their team relegated.
In tears, barely consolable, it's all laid bare, and that's just the adults.
Take it on the chin? Oh well, never mind, what's for dinner and a good night's sleep before cheerfully tripping off to work the next morning? Forget it.
Three assumptions of late have shown how shaky is the ground on which many of them are founded.
A few weeks back, Manchester City's Premier League campaign had hit the skids. From setting the pace for much of the season, they had slipped eight points behind their most bitter, and geographically closest, rivals.
Manchester United seemed to have the defence of their crown all but settled. Another couple of wins against lesser opponents and the games left/points available equation would have made catching up impossible.
The fun to be had at the blue half of their city could begin. Even Manchester City's Italian coach Roberto Mancini had chucked it in. It can be a funny old thing, sport.
Instead, early today, barring something simply inconceivable - here we go again - City will have wrapped up their first English league crown for 44 years. All they needed to do was beat battling Queens Park Rangers at their own Etihad Stadium, at which they have won 17 of their 18 league games this season, and drawn the other.
QPR needed a point to be sure of their place in the league next season and relegate Bolton Wanderers. No problem with incentive then.
Manchester City prospered because Manchester United, inexplicably, lost at lowly Wigan and drew at home to capable Everton, despite leading by two goals going into the last 10 minutes, while City, at the same time, rediscovered the attacking verve which produced 90 goals from their first 37 league games. No one saw that turnabout coming.
Think, too, of the Crusaders. Certainly, they were off colour in edging past the defending champion Queensland Reds eight days ago.
Even so, who'd have seen them being outplayed by the unloved Melbourne Rebels by nine points on Saturday night, and being kept scoreless through the second half?
There are some rumpty teams in the Super 15, but the Rebels, coming from the southern AFL stronghold, are always marked down as a must-collect four, or five, points.
The Crusaders left key players on the bench. Disrespecting the opposition, taking liberties, it all came back to sting the most successful, respected franchise in Super rugby history.
The assumption? That there's no need to fret; the Crusaders will be there or thereabouts at the sharp end of the competition.
As it happens, the Crusaders have plenty of credit left in the bank of expectation. The assumption still has weight, if not being cloaked in the familiar layer of damn-near certainty.
The Highlanders and Hurricanes are hard on their tails in the New Zealand Conference. The run-in promises to be a thriller.
Then there's the windsurfing community. It might be an Olympic sport for just one more Games, in London this year, after the International Sailing Federation voted to bring in the visually exciting, if more dangerous kiteboarding for Rio de Janeiro in 2016.
The vote was tight, 19-17, and now the Spanish federation have'fessed up and said they got their vote wrong, misunderstanding the process, which effectively makes it 18-all. There is far more water to swish beneath the boards before this is finally settled.
But the point is, the international windsurfing body are thought to have got a touch cosy, assuming that although they faced a challenge, they'd be all right on the day.
Maybe they didn't lobby as hard, or see the threat as clearly, as they ought.
If true, it's something they have in common with Manchester United and the Crusaders.
Melbourne Rebels. The Super 15 easybeats (well, one of them anyway) turned over the Crusaders. Who'd have thunk it.