Ask any of the top ATP stars today, and they will tell you that the ATP Finals is a major title in men's tennis.
In fact, behind the Grand Slams, it is the title to win. You have to earn your way into it by finishing in the top eight of the world rankings at the end of the season and it carries the prestige of everyone knowing you can only win it by beating the best of the best.
However, in recent years winning it has seemingly come with a 'curse' that almost every player is struggling to break - and Alexander Zverev is no different this season.
Andy Murray - 2016
If there is indeed a curse attached to winning the ATP finals, then nobody has felt its fury quite like Andy Murray.
Murray qualified for the tournament as the world number one after a simply brilliant season. It was being held in London, ensuring a partisan home support, and both Rafael Nadal and Roger Federer were both missing from the line-up.
When he won it, no one was surprised. Murray even beat Novak Djokovic in the final with relative ease.
However, the following year Murray's career came crashing down around him. A hip injury set in and he withdrew from the tour after Wimbledon.
Those injury problems persisted for two years, and they still hold him back to this day.
Grigor Dimitrov - 2017
In 2017, Bulgarian Grigor Dimitrov appeared to have the tennis world at his feet.
He was 25 and entering his peak years and had earned the nickname 'Baby-Fed' due to how reminiscent his game was to that of Roger Federer. At that time, and indeed any time, there was no greater compliment in tennis.
Dimitrov entered as the world number six and was helped by top seed Rafael Nadal having to pull out of his group after his opening match.
He had another stroke of luck as David Goffin stunned Roger Federer in the semi-finals. Dimitrov won the final against the Belgian and finished the year as world number three.
At that point, Dimitrov was expected to kick on and become a major force for years to come, but it just didn't happen.
A year later he was down to number 19 in the world rankings and by the end of August 2019 he was as low as 78.
He has rebounded slightly since and got himself back in the top 30 picture, but that 2017 ATP Finals was, at the time of writing in 2022, the last title he won on the ATP Tour. Cursed!
Alexander Zverev - 2018
Alexander Zverev had been heralded as the next big thing in tennis ever since he broke through as a teenager. At the end of 2018 and at the age of 21, it looked like he had truly arrived.
Zverev was in Djokovic's group and lost their round robin match, but he got revenge by beating the Serbian star in the final.
To make things even tougher for Zverev, he had to play Roger Federer in the semi-finals. That means he had to beat both Djokovic and Federer to win the title - and he did.
Like Dimitrov before him, Zverev was expected to be a major player the following year, but that never happened. His decline was not as dramatic as Dimotrov's, but it was still quite pronounced.
Zverev managed to win just one title in 2019, and even that was just an ATP 250. It was his worst season since his very first on the ATP Tour and it took him a long time to turn that around.
Stefanos Tsitsipas - 2019
There was yet another first-time winner of the ATP Finals in 2019 as Stefanos Tsitsipas scored a real underdog victory.
It was the first time in a while that all three of Rafael Nadal, Roger Federer and Novak Djokovic played, and Daniil Medvedev was starting to seriously emerge too after reaching his maiden Grand Slam final that Autumn.
Tsitsipas had a tough draw too, having to face Nadal, Medvedev and Zverev in the group, but he came through it impressively.
Federer came next in the semi-finals, and he won that too before beating Dominic Thiem in the final.
It is still Tsitsipas' biggest title of his career but, like Zverev, he struggled greatly the following season.
In fact, he also managed to win just one solitary ATP 250 title the following year although, in fairness to him, it was a hugely disrupted campaign due to the Covid-19 pandemic.
Daniil Medvedev - 2020
There is always an exception that proves the rule, and in the case of the ATP Finals winners' curse rule.
The new world number one did it in massive style too, beating both Nadal and Djokovic on his way to winning what was, then, this biggest title of his career.
Medvedev has no issues building on the title in 2021 either, defying the curse to reach two Grand Slam finals and winning one of them - the US Open.
As things stand today, he has continued that progress by toppling Novak Djokovic to be just the fifth ATP world number one in 18 years.
Alexander Zverev - 2021
Zverev bounced back from the curse to seriously re-establish himself in 2021 and he was looking like a major contender again by the time the ATP Finals came around.
That season he had won five titles by the time he arrived in Turin for the ATP Finals' first edition at their new venue.
They were big titles, too. He won two Masters events in Madrid and Cincinnati before claiming Olympics gold in Tokyo.
No one was surprised, then, when he won his second ATP Finals title. He was hitting big, serving bigger, and winning tournaments.
2022 has been a bit of a disaster for Zverev so far, though, suggesting the curse is still very much a thing.
He flopped at the Australian Open, failing to even reach the quarter-finals of a tournament many experts and analysts expected him to win.
Zvevev then lost in the final of the ATP 250 in Montpellier to world number 35 Alexander Bublik, but the biggest blow was still to come.
He was defaulted from Acapulco - a tournament he won in 2021 - for a violent outburst against an umpire's chair, whilst the umpire was still in it, during a doubles match.
Zverev has been fined for the incident, lost ranking points, and is in danger of tougher sanctions. If you're wanting to prove the curse is over, that's really not a very good start.