Hindsight is a wonderful thing, especially in football.
The game is full of 'what ifs?' - and that is certainly the case when it comes to buying and selling players.
Every fan knows of one great player they wish their club could have held on to - Kevin De Bruyne at Chelsea, or Jadon Sancho at Manchester City, for example.
Those are perhaps some of the highest-profile cases of teams seriously overlooking the talents of a certain star.
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So, let's get into it.
Arsenal - Serge Gnabry
When Gnabry left the Gunners for Werder Bremen in 2016, very few eyebrows were raised.
After all, this was the youngster that couldn't break into the first team and went on-loan to West Brom, where he played just THREE games.
But fast forward three years and Gnabry is now one of Europe's hottest properties and he's ripping up the Bundesliga with Bayern Munich. How Arsenal could do with him now.
Aston Villa - Marc Albrighton
'This was laughable' says The Irish Guy. After Albrighton was released by Villa in 2014 and told he wasn't good enough, he went on to join Leicester and win the Premier League.
The winger played EVERY SINGLE game in their title-winning campaign, while Villa, with Scott Sinclair out wide, were relegated to the Championship that same year.
Bournemouth - Tyrone Mings
Mings played just 17 games for Bournemouth after arriving for £8 million in 2015. He didn't make an impression on the south coast but has become a £20 million rated England international at Villa.
Just imagine Mings and Nathan Ake in the same backline this season.
Brighton - Fikayo Tomori
Chelsea sent Tomori on-loan to Brighton in 2017, where he made just nine Championship appearances as a 19-year-old.
The club had a chance to either extend his loan or even buy the defender the following summer but did neither. Now, he's a Chelsea regular and at 21, already has an England cap.
Burnley - Shane Duffy
Duffy was another loanee who wasn't given a chance by his temporary club in 2011. He made just one appearance for Burnley before returning to Everton.
But now, he's a regular Premier League centre-back with Brighton, having made 80 appearances in England's top flight.
Chelsea - Kevin De Bruyne
Where do we start with Chelsea? There are so many players the club has overlooked - Kylian Mbappe and Mohamed Salah to name a few. But the worst is De Bruyne.
After leaving Stamford Bridge, the Belgian impressed in Germany before joining Man City for £55 million. He's since become the most dangerous midfielder in the Premier League and won seven major trophies in four years.
Crystal Palace - John Egan
In 2012, Palace had Egan on-loan from Sunderland. But he didn't get a real chance, playing just once in the FA Cup.
Had the Eagles shown a little more faith, Egan would be in their backline, rather than forming a solid centre-back partnership at Sheffield United, where he's been winning plenty of plaudits.
Everton - Eric Dier
Dier has played over 200 times for Spurs, featured in a Champions League final and even scored an important penalty for England in the World Cup.
But he could easily have been featuring for Everton, had they not overlooked him in 2011, where they played him in the under-18s during his time on-loan from Sporting Lisbon. Ouch.
Leicester City - Chris Wood
Of course, Leicester have done just fine without Wood. But after moving to Leeds for £3m, the striker scored 30 goals and earned himself another chance in the Premier League with Burnley.
Foxes fans won't have too many regrets about letting him go, but Wood could have been a decent option off the bench for Jamie Vardy.
Liverpool - Iago Aspas
He didn't make an impression at Anfield, but Aspas is a solid goalscorer. Since leaving Liverpool, he's returned to La Liga, where he's netted over 100 goals and even won the Europa League.
Aspas has also been named in two Spanish Team of the Seasons and even scored at the 2018 World Cup in Russia.
Manchester City - Kieran Trippier
The Irish Guy has named Trippier over Sancho because he believes Man City didn't really overlook the latter.
They did everything they could to keep him, bar starting the teenager over the likes of Raheem Sterling and Leroy Sane while chasing Premier League titles.
So Trippier is a fair shout. After three years in the academy, he was sold for £2m but has since gone on to play for some of Europe's biggest clubs and score in a World Cup semi-final.
Manchester United - Wilfried Zaha
Zaha just edges Paul Pogba in terms of United's most overlooked player. The winger made just two appearances for the club but is now one of the league's most skilful and dangerous players.
While Zaha is no longer at Old Trafford, Jesse Lingard has gone on to make 185 appearances in his place. Unlucky, United fans.
Newcastle - Florian Thauvin
Thauvin played 13 games for the Toon and failed to impress between 2015 and 2017. But he's since gone on to score 63 goals for Marseille and play in France's World Cup winning team.
Norwich City - Harry Kane
Norwich had Kane on their books during the 2012-13 season.
The club were battling relegation and didn't want to risk playing an unknown youngster, so Kane sat on the bench behind Steve Morison and Grant Holt, playing just 150 minutes for the club.
He's since gone on to become one of the Premier League's best strikers, win the Golden Boot and captain England. It seems likely he'll soon become his nation's all-time leading goalscorer, too.
Sheffield United - Aaron Ramsdale
The Irish Guy reckons Ramsdale will one day go on to become England's regular goalkeeper. At 21, he's holding down a first-team spot at Bournemouth and looks on course for a call-up.
Yes, the Blades have a promising young England goalkeeper of their own this season, but he's only on-loan from Man United. Had they kept Ramsdale, they'd have a promising talent of their own.
Southampton - Martin Caceres
The Saints haven't overlooked many, but Caceres certainly slipped through the cracks.
He played just once for Southampton but was good enough for more of a chance at Barcelona, Sevilla and Juventus. It's certainly a strange one.
Tottenham - Jermaine Defoe
Spurs waved goodbye to a proven Premier League goalscorer when he moved to MLS in 2014. Meanwhile, Roberto Soldado took his place up-front.
The Irish Guy claims Defoe left way too early and that the move away from Spurs 'made no sense to anybody'.
Watford - Britt Assombalonga
Assombalonga has become a solid goalscorer since leaving Watford, where he was given just four games to prove himself.
After leaving, he's netted over 60 Championship goals and right now, the Hornets could really do with a striker capable of doing that.
West Ham - Victor Moses
In 2015, Moses looked like a bang average winger and was shipped out on loan by Chelsea to West Ham. There, he spent most of the time on the bench, scoring just once.
The Hammers decided against making the move permanent and just 12 months on, Moses featured 34 times at right wing-back in the Premier League as Chelsea stormed to the title. Madness.
Wolves - Nathaniel Mendez-Laing
Wolves fans won't lose any sleep over their club selling Mendez-Laing. He made a grand total of zero league appearances but has since gone on to play pretty well for Cardiff.
The Midlands club, of course, are doing well without him anyway. Clearly, they don't overlook many players!
Well, what a decade it's been. Hindsight is a wonderful thing and we can now see that some Premier League clubs made big mistakes over the last 10 years.
Chelsea, Arsenal and Man United are perhaps the most guilty parties.
But just imagine how different things would have been if Norwich kept Kane, or if Everton held on to Dier. Would those two be as successful as they have been? Perhaps not.News Now - Sport News