This time next week, Fernando Alonso will no longer be a Formula One driver. For many in the sport there is a great deal of frustration in that fact, fuelled by an overwhelming sense of 'what if?'
What if Alonso found his way back into a competitive car? Would he then be fighting Lewis Hamilton for the title at the final round of the season this weekend? And would that mean he'd be staying in the sport for at least two or three more seasons?
Ultimately, how much unrealised potential will be leaving Formula One on Sunday night?
Ahead of Alonso's August announcement that he would walk away the sport at the end of the year, F1's bosses tried to encourage him to stay. There was no chance of getting him into a Mercedes or a Ferrari in 2019, but such is Alonso's appeal among F1's fanbase that it was better to have him on the grid -- even in an uncompetitive McLaren -- than racing elsewhere.
It led to suggestions that, perhaps, the sport had let Alonso down. Sure, he had made poor decisions when moving between teams, but a driver of Alonso's ability should not be finding himself at the peak of his powers without a competitive car.
However, the man himself says that is missing the point of his decision.
"No, I think this is a mistake a lot of people are taking from this decision," he told ESPN in a recent interview. "I explained it very clearly in my statement: I am stopping Formula One because there are other bigger challenges outside Formula One than the ones I can see here.
"It's not because I am not winning here, I could sign for a competitive team next year, maybe not the top two, but maybe the third one. But I say no because I arrived in F1 17 years ago and I have won two world championships. I have won more races than what I dreamed of when I came here and this part of my career is done -- it was a success. I have ticked the box. I need to go for another tick and find another box to fill. That's the only reason.
"If I had only done five or six seasons in F1 and I still had a lot energy, I would stay despite the results -- better or worse -- but after 17 years and after achieving everything here, I think it's the right moment."
The first of the "bigger challenges" Alonso is chasing is the Indianapolis 500 next year. Having won the Le Mans 24 Hours this year and the Monaco Grand Prix two times earlier in his career in 2006 and 2007, Alonso would secure motorsport's unofficial triple crown with an Indy 500 win. It's a feat that has only been achieved once before by Graham Hill and Alonso sees it as a way of underlining his talent in motorsport's history books.
His triple crown aspirations first became clear towards the end of 2016. After a second year in an uncompetitive McLaren-Honda, his long-held ambition of a third world title looked more distant than ever. He'd left Ferrari two years earlier convinced the Italian team would not be able to challenge for a title in the foreseeable future and was lured back to McLaren by the promise of Honda's return to the sport.
There were no guarantees the new McLaren-Honda partnership would be successful, but in his mind in 2014 it had more potential than Ferrari, which had failed to deliver him the fastest car on the grid for the past five years. He had come close to a championship victory in his first year at Maranello in 2010 and again 2012, but 2014 had been a big step backwards for Ferrari and Alonso was no longer convinced the Italian team could deliver what he wanted.
His relationship with Ferrari's new team principal at the time, Marco Mattiacci, was also becoming increasingly frosty, and there was also the not-insignificant fact that McLaren was offering him even more money. Stirred by the prospect of driving for a reborn McLaren-Honda team like the one he had seen win championships with Ayrton Senna and Alain Prost when he was growing up, Alonso jumped at the opportunity to leave the Italian team and join McLaren.
With the benefit of hindsight, it was the wrong decision. The McLaren-Honda project started slowly in 2015, stuttered forward in 2016, but took another backwards step in 2017 -- bringing the relationship between team and engine supplier to crisis point. McLaren, encouraged by a frustrated Alonso, then split with Honda at the end of year only to find its 2018 car was still off the pace with Renault power this season. In that same period, Ferrari has gone from strength to strength, and for the past two seasons has had a car capable of challenging the dominant Mercedes team for the title.
Knowing what he knows now, surely it's only natural for Alonso to have regrets?
"Not really," he says. "Obviously if you know the results in advance you maybe do things differently. But I had to go to Ferrari in 2009, I had this opportunity and everyone wants to go to Ferrari. Ferrari wasn't competitive but I still had good fun -- I was still fighting for a lot of championships until the last race.
"And then in 2015 the Mclaren-Honda combination was attractive and everyone was agreed here in the paddock it could be a success, so I joined that project with a lot of hopes and a lot of commitment and I think we didn't succeed. But we're still doing a decent job in recovering and never giving up.
"From 2009 when I left Renault, Renault never won a championship from that moment so it's not that Renault is dominating the sport. When I left Ferrari in 2014, they never won a championship from that moment so it's not they are dominating the sport. Every step I did, I didn't succeed but also the team I left didn't succeed.
"I don't understand the people that think I made the wrong choices constantly because with all of my last choices, they're still not winning."
But there are many that think Alonso in this year's Ferrari would be winning. There are many that are convinced he would not have made the same number of mistakes as Sebastian Vettel this year and that the title would be going down to the final round in Abu Dhabi with Alonso at the wheel.
"These are just hypothetical cases," he says in response. "You never know. For sure I fought with much worse cars until the last part of the championship with Ferrari, but maybe one year you have a competitive car and you're unlucky at a couple of races and you're not fighting for the championship anymore.
"I am happy. I am happy, and as I said, these 17 years, especially when you take the decisions you take, it's because you believe they were the right ones. You never take a decision thinking this could be wrong, you take it because you believe it's the right one. If I go back without the crystal ball, I would take the same decisions."
Could he return?
Throughout his struggles in an uncompetitive McLaren this year, Alonso has been keen to stress that the lack of a quick car is not his reason for leaving F1. He has talked a lot about how "predictable" modern F1 is compared to when he started racing in the early 2000s and how boring it has become as a result. That has often been dismissed as Alonso looking for excuses to get out of his current situation at McLaren -- after all, Ferrari was as dominant in the early 2000s as Mercedes is now -- but dig a little deeper and he reveals why so much of the pleasure he used to derive from F1 has been removed.
"The rules change went in the wrong direction," he says, "because now the teams have very little room to play and to use creativity into strategies or anything like that. There is fixed fuel for everyone, a fixed fuel flow to put in the engine that is the same for everyone. The same tyres for everyone, the same weight distribution for everyone. The same tyre pressure, mandatory for everyone, the same camber for everyone.
"In a way it helped the less talented people. They train a lot in the simulator, they arrive to the new circuits knowing exactly where are the bumps, where are the kerbs that you can take, where are the difficult spots and then into the race, normally there is only one optimum way to arrive to the end.
"It's all about how to save the energy, the tyres, whatever that the engineers tell you to do, you just follow that instruction. You have a little bit of room for instinct in different parts of the race but normally it's less optimum if you try to do it yourself. I think when we didn't have all that information it was more you and the car on a Sunday afternoon and I think it was more about driver input."
Alonso believes those in charge of F1 are aware of these issues and he is "optimistic" they will "make some big changes" to address them under the next major regulation rewrite in 2021. So the obvious question is could that tempt Alonso back? His announcement in August left the door open to a return to F1 in the future and his old teammate Kimi Raikkonen has just signed a contract to stay in F1 for two more years until he is 41. So is there a chance a 39-year-old Alonso could line up on the 2021 grid ready to do battle in cars that are more exciting to race and offer more reward for driving talent?
"I don't think so," he says. "I think at that time, 2021, it will be a little bit too late. I don't know for certain because it's difficult to know how you will feel in two weeks' time, so I don't know in two years' time, but to have the energy to start back up and to put full dedication and full commitment to something when you're 39 or 40 years old ... it's going to be more difficult than now. I am not planning that."
So make the most of Alonso in F1 this weekend. His Abu Dhabi Grand Prix is unlikely to go down as one of the greatest of his career given the car he will be driving, but he has no plans to come back once it is over. After that we'll just be left with the frustrating question of 'what if?'