Often money serves as the explanation for a failed transfer, with clubs either not agreeing on a fee or the player feeling his demands are not being met.
But sometimes, the real reason is far more complex. For example, why Diego Maradona never ended up at Bramall Lane is a fascinating tale.
Here talkSPORT.com takes a look at the weirdest examples of why certain deals never got over the line ahead of the January window...
Zinedine Zidane
In 1995, Blackburn Rovers were on the crest of a wave, with owner Jack Walker's dream realised.
Rovers beat Manchester United to the title and a bright future seemed to be ahead of them with Zinedine Zidane on Kenny Dalglish's wishlist.
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Zizou was impressing in France with Bordeaux and emerging on the international scene when Blackburn made their move.
Christophe Dugarry was also part of a potential deal for the Ewood Park outfit as they looked to complement Alan Shearer and Chris Sutton.
Blackburn owner Walker, though, had other ideas and despite the duo flying to the club for talks, they were never signed.
"Why do you want to sign Zidane when we have Tim Sherwood?", was what Walker reportedly said about the transfer.
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Zidane and Dugarry spent another campaign with Bordeaux before joining Juventus and AC Milan, respectively.
Virgil van Dijk
Neil Warnock almost signed the Liverpool centre-back only for Crystal Palace to pull the plug on a deal due to fears he lacked pace.
The veteran manager wanted to bring Van Dijk to Selhurst Park from Celtic in 2014 but the deal was blocked.
"Van Dijk - I'm delighted he's playing like he is," said Warnock.
"We could have bought him at Palace for £6million but my chief scout told me he was too slow. I think he's still in a job as well!"
A year later Van Dijk arrived in England at Southampton but it's at Liverpool where the Dutchman showed just how silly the pace assessment was.
During Liverpool's Champions League triumph in 2018/19, Van Dijk recorded a 34.5km/h sprint in a 3-0 defeat to Barcelona, which was a faster speed that season than Leroy Sane, Kyle Walker and even Kylian Mbappe.
Michael Essien
The Chelsea great had been on trial at Burnley as a teenager after impressing for Ghana in the Under-17 World Cup.
But the Lancashire club passed on signing him after refusing to budge on their policy of paying more than £60-a-week for an apprentice.
In 2009, former Burnley chairman Brendan Flood said in The People: "I discovered Michael Essien had been on trial here for a few days.
"One of the best players in the World Cup - and we hadn't signed him.
"The club policy meant we wouldn't pay an apprentice more than 60 quid a week.
"It smacked me in the face that the problem was a lack of communication within the club that stopped our youth guys making an exception to the rule."
Pep Guardiola
The Spaniard was a top midfielder, who spent most of his career at Barcelona, and has been even more illustrious as a manager.
Guardiola has dominated in the Premier League as a manager but English football never got to enjoy him as a player, though not for lack of trying.
Paul Jewell attempted to lure him to Wigan in his mid-30s while Stuart Pearce also wanted him at Man City but the Spaniard was deemed too old.
Speaking in 2018, he revealed the Latics' attempts, but said: "I wasn't good enough!
"That is the truth. I was old, really old as a football player. I knocked on the door, I tried to come here to play in English football as a player but I was not able.
"The same happened here at Manchester City when I came here with Stuart Pearce. They were so clever! I was not good enough."
Robert Lewandowski
The Polish captain's career could have been very different if the Eyjafjallajokull volcano in Iceland had never erupted.
Blackburn again had a deal all-but done to sign the now Barcelona sensation 13 years ago when he was making his name at Lech Poznan.
"I went with my chief scout Martyn Glover and it was quite a trip," then-Blackburn boss Allardyce told talkSPORT.
"We were very impressed with the player, the chairman did a deal for about €8million with the club and he was due to fly over.
"The ash cloud started in Iceland and all flights got cancelled, so he couldn't get on the flight.
"We were waiting for him at Manchester airport and then a week or two later he signed for Borussia Dortmund.
"I didn't remember this until reading an article and Lewandowski brought it up. It just reminded me how close we came to one of the world's top goalscorers."
Pierre-Emerick Aubameyang
The former Chelsea striker scored a hat-trick against West Brom while playing for Arsenal in 2021 and it so happens that he almost ended up banging them in for the Baggies.
Stuart White, a former club scout, recommended Aubameyang to the Midlanders back in 2011 after he impressed for Saint-Etienne.
"I had been to Dijon on a Friday night to watch one player in particular, a centre forward who didn't impress me at all," White told Planet Football.
"My 'bonus game' before flying home on the Sunday was Auxerre v Saint-Etienne on the Saturday night.
"Saint-Etienne drew the game 2-2, but Aubameyang and Emmanuel Riviere were tremendous as a pair.
"I came back raving about Aubameyang, and as luck would have it his agent called me the following week, probably because he'd got to know that I had been at the game
"He was obviously calling many clubs, but the lad was then a Milan player on loan at Saint-Etienne and he was interested in coming to England.
"The outline deal was explained to me and it was clear that he was going to be affordable so I recommended that we pursued it.
"On the back of my shout, a few more of our scouts went out to watch him a week or two later and he scored an early goal against Sochaux in a 2-1 defeat but didn't impress sufficiently on the night, which can happen.
"He then went back to Saint-Etienne, scored 21 in 45 and was subsequently sold to Dortmund for 13million euros. He would have been a free loan to us with a two million euros fee tied into the deal had we taken him."
Andriy Shevchenko
Shevchenko himself has publicly denied having ever had a trial at West Ham, but Harry Redknapp claimed he rejected him when he was in charge.
Redknapp said in 1999: "I was offered him about four years ago when he was only 19.
"We had him over for training for three or four days and I remember watching him play for us in a game against Barnet reserves at Chadwell Heath.
"He didn't pull up any trees but looked decent enough. But this was just after I had had all those problems with the Romanian lads and I thought the last thing I needed was a Ukrainian.
"Besides, they were asking around £1million for him and I didn't have the money at the time."
Diego Maradona
He was at his brilliant best when playing for the national side and at Napoli, taking the club from an unfancied Italian outfit to two Serie A titles.
But it could have been Sheffield United who reaped the benefits of Maradona's magic, as they came so close to signing him in 1978.
The Blades, a second division side at the time, flew with representatives from Tottenham on a scouting mission to see what talent they could find in the South American nation, claim Yorkshire Live.
Then-United boss Harry Haslam and director John Hassle joined Spurs counterpart Keith Burkinshaw and his party on a flight to Buenos Aires.
United already had deals in place for Alejandro Sabella and Pedro Verde but after watching Maradona in training, Haslam was reportedly 'mesmerised' by Maradona and promptly said: "I'll take him, how much?"
A £150k deal was agreed between the Blades and Argentinos Juniors, but the move collapsed following an unlikely intervention that evening.
Haslam was reportedly greeted at his hotel room door by members of Argentina's notorious military police, a right-wing coup that had overthrown the previous president.
The junta were happy to let Maradona leave the country but only if Sheffield United paid them £150,000 on top of what they were already going to pay Argentinos Juniors.
United were still willing to shell out on the 17-year-old but they were uncomfortable making the deal political and the move was off.
Lionel Messi
The Argentine's incredible Barcelona career was very nearly scuppered by one of the most audacious loan bids ever, thanks to the Football Manager obsessive son of Alex McLeish.
"My son Jon was into Championship Manager," he explained to The Big Interview.
"He was constantly giving me names in South America. They come out the sky and say 'Lionel Messi is going to be the best player in the world'.
"You dismiss it but Rangers were downsizing and we were looking for some quality in midfield.
"Barry Ferguson had gone down to Blackburn so we lost a guy who would have taken the ball in any stadium anywhere in the world. We needed players of that ilk again.
"Jan Wouters phoned Henk ten Cate, who was the assistant of Frank Rijkaard, the ex-Dutch international.
"Jan phoned him and said: 'Messi?' We were told no chance."
Bamba Dieng
Leeds' desperation to sign a striker on deadline day of the 2022 summer window saw the Whites strike a deal with Marseille for the Senegalese forward.
The Premier League club were ready to pay £8.6m for Dieng and the player was sat in an airport waiting for a private jet to take him to England.