Everton have often been guilty of selling players too early, with the Toffees youngsters often going on to have successful careers elsewhere despite failing to make an impact at Goodison Park.
Ellis Simms is the latest example after his 13-goal season with Coventry City in the Championship, following Ademola Lookman in excelling away from the club.
The club undoubtedly made good money on the pair after selling them for £8m and £16m respectively, but, given Everton's tally of 32 goals in 31 games, the Toffees could've benefitted from keeping the duo.
Another player who departed Goodison in 2023 is a talent who is thriving in one of Europe's top five leagues, with Everton potentially regretting his departure for a minimal fee.
Niels Nkounkou stats at Everton
After joining the club for £240k from French side Marseille back in the summer of 2020, young full-back Niels Nkounkou originally arrived on Merseyside linking up with the club's youth sides.
However, he would go on to make two appearances in the Premier League during the 2020/21 campaign, making his English top-flight debut in the 2-1 defeat against Newcastle United.
33. Robin Olsen
2. Jonjoe Kenny
13. Yerry Mina
5. Michael Keane
18. Niels Nkounkou
16. Abdoulaye Doucoure
8. Fabian Delph
6. Allan
10 Gylfi Sigurdsson
21. Andre Gomes
9. Dominic Calvert-Lewin
He would fail to feature in the Premier League for the Toffees during the opening month of the 2021/22 season, subsequently joining Belgian side Standard Liege on loan until the end of the campaign.
Nkounkou played 23 times during his stint in the Belgian Pro League before two more temporary spells away from Goodison Park in the following season.
He joined Cardiff City for the first half of the campaign, but it was his period at Saint-Étienne that caught the eye and saw the youngster make his first breakthrough in professional football.
The French left-back made 20 appearances between January and May, scoring six times and providing eight assists in Ligue 2 – a remarkable return for a defender.
His sensational form for the French outfit saw the club decide to permanently purchase Nkounkou, with the 23-year-old joining Saint-Étienne for just £1.8m last summer.
Niels Nkounkou's market value in 2024
Less than a year after his £1.8m departure from the Toffees, defender Nkounkou has seen a rapid rise in his market value after a shock move to Germany.
Just a couple of weeks after his permanent move to Saint-Étienne, the youngster completed a £9.4m move to Bundesliga side Eintracht Frankfurt, with Everton selling the Frenchman at a bargain given his recent transfer fee.
He's now valued at £17m, as per CIES Football Observatory, with the left-back's value receiving an 844% increase from the £1.8m fee Everton sold him for last summer.
Nkounkou has since registered three goals and three assists for Frankfurt following his move, with the 23-year-old evidently enjoying life away from Goodison Park.
Given his form and rapid increase in market value, Sean Dyche's side must wish they kept hold of their former talent, with Nkounkou potentially providing valuable squad depth at left-back in a season where the club are battling relegation once more.
He's shown he's capable of producing consistently in one of Europe's biggest divisions, with the Toffees potentially living to rue their decision to sell him for a cut price.
Market Movers
Football FanCast's Market Movers series explores the changing landscape of the modern transfer market. How much is your club's star player or biggest flop worth today?