Why did Arsenal fail to show up for their first game of the season, given their new status as title challengers?
How did they lose at home to West Ham United but then, yesterday, beat a stronger Crystal Palace side away from home?
More often than not, in football, the simple answer is the right one: Alexis Sanchez is back.
This was not peak Sanchez, the player who ripped through the Premier League in the first half of last season before taking Chile to this summer's Copa America. But a rusty Alexis Sanchez is still a special player who can decide games, as he did here.
Sanchez didn't return to pre-season training at Arsenal until a fortnight ago. Arsène Wenger revealed that the player had been working at home in Chile before then, allowing him to come back "reasonably fit".
However, this meant that Arsenal did not quite have the benefit of Sanchez's usual technical skill. He missed four first-half chances as Arsenal squandered the opportunity to kill the game before Crystal Palace could even get into it.
There is far more to Sanchez, though, than his touch and execution, as good as they are.
He is also one of the Premier League's fiercest and bravest competitors, a man described by Wenger last week as a "hyperactive guy" who can always be relied upon to give his full commitment to anything he tries.
This was the Sanchez who played for Arsenal yesterday, with his voracious competitive appetite and explosive physical power.
This was the Sanchez who shredded Palace with his first-half movement - even if he could not quite capitalise upon it - and who eventually won Arsenal the game.
It was 10 minutes into the second half, the teams were level at 1-1 and Palace's Connor Wickham had just hit an upright.
The noise and the momentum was all with the home side, who were threatening to seize control of the game.
Then Arsenal broke and Aaron Ramsey fed Hector Bellerin, who stood a cross up to the far post.
Joel Ward should have nodded the ball away but Sanchez bounded up and thumped a header towards goal. Damien Delaney, trying to clear it, sliced the ball into the net.
As it happens, Sanchez's header was going wide. But that is the desire and the athleticism - independent of his skill - that sets Sanchez apart, and that won Arsenal the game.
"He brings a drive forward, the pressure on the opponent, goal chances," Wenger said. "When it was 1-1, it is not a coincidence that Sanchez found the header. It is a typical Sanchez goal, more desire than fitness. He is still a bit short but he is a fighter."
Wenger was delighted with a win that showcased enough aspects of the game - flowing football in the first half, dogged defence in the second - to almost make up for their non-performance at the Emirates.
This was not quite a complete display, but there was a lot to admire about it, not least the seriousness and the focus it showed.
Arsenal began the game playing incisive football that was as far removed as imaginable from what happened against West Ham.
Mesut Özil - whom Wenger described as "absolutely magnificent" - broke forward and put Sanchez through, and with more match fitness he would surely have scored.
Undeterred, Arsenal kept probing and scored an opening goal of remarkable quality.
Sanchez found Özil out on the left, and he drove a left-footed cross back into the box. Olivier Giroud, with his back to goal, jumped and unleashed an acrobatic overhead kick which flew beyond Alex McCarthy and into the far bottom corner of the net.
This was when Arsenal should have killed the game but the one-twos and flicks did not quite come off and Sanchez had one low shot saved and mistimed another header over the bar.
It was, therefore, immensely frustrating for the visitors when Ward equalised out of the blue, striking a Wickham knock-down into the bottom corner of Petr Cech's goal from 25 yards. Laurent Koscielny turned his back on the shot.
This was when Arsenal were threatening to wilt and Francis Coquelin was certainly fortunate to complete the first half, having tripped Wilfried Zaha immediately after being booked for a similar foul on Yannick Bolasie.
Palace came out strongly in the second half, getting the ball wide early and often, with Yohan Cabaye directing play on his home debut.
Had Wickham converted Zaha's cross three minutes after the re-start it would have been a different game.
But Sanchez put Arsenal back into the lead - with help from Delaney - and from there Wenger's side, to their manager's pleasure, dug in to see out the win.
Mikel Arteta, easing his way back after eight months out, came on for Sanchez and made one crucial intervention when Lee Chung-yong was about to equalise.
Alan Pardew had also thrown on Jordon Mutch, who missed Palace's best late chance when he could not successfully direct his header the ball after the ball was flicked on to him. Ward, who scored Palace's goal but lost Sanchez for the winner, could only nod tamely at Cech from a last-minute corner.
Sanchez, by that point, was on the bench, topless, content to see his efforts rewarded with three points. He trudged off at the end knowing that there is far more to come. © Independent News Service.