Unai Emery very rarely has perfect days. His Arsenal team are akin to James McAvoy's character in the film Split. In the film, McAvoy plays a man with split personality disorder - hence the very clever title - who has 24 different personas all striving to dominate his consciousness.
Emery's Arsenal are similarly volatile, in the sense that you never know what version of the Gunners you are going to get on any given day. There's lazy Arsenal, brilliant Arsenal, naive Arsenal, crazy Arsenal, stupid Arsenal, beautiful Arsenal...the list goes on.
Occasionally, very occasionally, Emery gets a break from his side's manic inconsistency and gets to sit back and relax, confident of side's ability to navigate the game without drama. The most recent instance of this eclipse-like rarity came against Nottingham Forest on Tuesday evening.
Facing off against the Championship high-flyers in the Carabao Cup third round, Arsenal breezed to a 5-0 victory courtesy of goals from Rob Holding, Joe Willock, Reiss Nelson and a brace from Gabriel Martinelli.
The emphatic result wasn't the only reason to be cheerful for the Gunners boss. Goal scorer Holding was making his first appearance for more than nine moths following a knee injury, whilst Hector Bellerin also returned to the side after rupturing his ACL in January.
Emery will also be impressed by the way Callum Chambers continued to catch the eye at right-back, but it was on the opposite defensive flank that another, far more interesting story was beginning.
The game marked the debut of left-back Kieran Tierney, whose hernia injury had previously prevented him from making an appearance for the Gunners after arriving in the summer.
Tierney's debut has been a long, long time coming, not just because of his injury, but also due to the long-winded transfer saga that pre-dated his arrival at the Emirate Stadium.
Even before Arsenal's interest was first reported in February 2019, the Gunners had been tracking the Scotland international for over two years, as he made a name for himself, starring for Celtic in the SPFL.
When the time eventually came to start the negotiations in the summer, the deal initially appeared unlikely to be completed. In typical Arsenal fashion, Celtic were reportedly outraged by the the Gunners' poultry first offer for the 22-year-old. They took particular grievance with the incentives-based structure of the deal.
Months of hearsay and rumour finally resulted Tierney moving to north London on August 8th - fractionally before the Premier League transfer window slammed shut - for a fee of around £25m.
The Scotsman's decision to leave Celtic was clearly bittersweet and he paid tribute to his time with the club be having 'Bhoys' embroidered on the boots that he wore against Forest.
"[Leaving Scotland] was the hardest decision in my whole life that I've had to make. I had to speak to my family and my close friends and my agent as well because it's a hard decision to leave a club that you love so much. People need to know that as well," he told the Daily Star.
Tierney's hernia problem meant he even had time to travel back up to Celtic Park in order to say a proper farewell to team mates and staff.
He finally returned to full training with the Gunners recently. The 21-year-old's rehab stepped up last Friday, as he featured for Arsenal's Under-23 side in a 2-2 draw with Wolves, and reports then surfaced over the weekend that suggested that the left-back could feature in the Carabao Cup. Reports that would prove to be correct.
The main question Arsenal fans were asking prior to kick off against Forest was whether Tierney's debut would be worth the wait. He answered these doubts resoundingly with a supreme first half performance full of energy, attacking intent and smart positioning.
His first major involvement in the game was a superb bit of a modern full-back play. Released down the left hand side Tierney was facing Matty Cash side-on from a standing start - seemingly with nowhere to go.
Yet, within a blink of an eye, the 22-year-old had flicked the ball past the Forest right-back and delivery a one-touch cross straight onto the head of Emile Smith-Rowe. It was sensational. A move straight out of the playbook of his compatriot, Andy Robertson. The Emirates crowd recognised this, exploding into thunderous applause for their new hero.
In his 77 minute stint on the pitch Tierney would attempt eight crosses and complete just over 30% of them. To put this into some sort of context and explain the Arsenal crowd's excitement at the full-back's start to life in north London, this is already more than Sead Kolašinac has managed this season, despite the Bosnian being on the field for over 200 more minutes.
It could be argued that if Kolašinac played in Tuesday's mauling of Sabri Lamouchi's side, he might have buffed his stats up to a more flattering level. I'm not sure though. Kolašinac is ultimately quite poor going forward, justifying his inclusion in the Gunners team with his resolute defensive attributes, but these are qualities that Tierney also possesses in abundance.
Tierney easily nullified the threats of Joe Lolley and Sammy Ameobi down the right flank and although the Scotsman will of course face sterner tests than the one he experienced on his debut, a 100% tackle success rate should not be sniffed at.
Perhaps the 21-year-old may even hold the key to Arsenal's problems with playing out from the back. Generally, Tierney looked calm and composed in possession, completing an impressive 84% of his passes.
His teammates were certainly impressed, with Pierre-Emerick Aubameyang and Alexandre Lacazette both sending their support on Instagram. Gunners' captain for the night, Rob Holding, was similarly effusive in his praise.
"I think he was brilliant, I loved having him on the left side of me. He was solid and for his first game back from a double hernia operation you can't ask for any more than that," he told football.london.
"He's good, a good Scottish lad who bring a bit of banter to the team. He and I are getting on really well, you couldn't ask for a better way for him to settle in."
This is all very encouraging but in Tierney's performance against Nottingham Forest was a start. Nothing more. The real hard work begins now, but if he keeps up this level of performance it won't be long until one of the most exciting, young, modern full-backs displaces the more traditional Kolašinac in the Gunners' starting XI.