The margin between success and failure can be tantalisingly small. Kyle Walker is one of the most promising players in the English game and the possible first-choice right-back at the European Championship, yet he was almost discarded by Sheffield United at 15 because he struggled to convince them he could be successful as a centre-forward.
Nearly seven years later, he is aiming to help Tottenham reach the FA Cup final for the first time since they won the competition in 1991. The 21-year-old has been one of the players of the season at White Hart Lane, his energy a vital component in Spurs' dynamic attacking.
Had it not been for the faith of two coaches, Ron Reid and Sam Safe, Walker admits he might now be "stacking shelves in a supermarket". It was Reid, then the academy director at Walker's home-town club, who decided the teenager had a talent that must not be wasted. Safe, a Sheffield coach affiliated to the Blades, realised that if Walker wished to move forward, he needed to take several steps back.
"I was 15 at the time, and I was the last of 14 young players to be given a scholarship at Sheffield United," Walker recalls. "I was getting worried, and my mum and dad were probably panicking more than I was, because they could see the bigger picture.
"I remember they pulled me into the office. There was Kevin Fogg and Ron Reid, the academy coaches at the time, waiting to speak to me. Kevin said that it wasn't his decision, but that Ron was going to give me a chance.
"I could see immediately that a big weight had been lifted from my dad's shoulders and he told me I was going to have to prove these people wrong.
"Then, when I was about 16, Sam Safe turned me into a right-back. I was [Spurs team-mate] Aaron Lennon's height, maybe smaller, at that age and playing up front, the centre-halves used to smash me. I was quick, so Sam thought my pace would get me out of a lot of problems.
"After playing at right-back for a while, I didn't want to play up front any more; it didn't interest me. I still speak to Ron Reid regularly. I need to thank him for putting the belief in me and I hope I've repaid him now because I could have been elsewhere, maybe stacking shelves."
Tottenham were one of the most impressive teams in the country during the first half of the season, yet since they lost 5-2 in the north London derby at Arsenal on 26 February, their form has slipped.
That defeat started a sequence of only one victory from eight Premier League matches. Before it Spurs were 10 points ahead of their rivals. Now they see Arsenal favourites to claim third place and automatic qualification for next season's Champions' League.
Tottenham have won two League Cups since they took the FA Cup in 1991 but the club are desperate to win one of the major trophies. Recent performances offer scant encouragement but victory over Chelsea today would give them momentum to maintain the push for a top-four finish.
As Walker tries to help revive his team, he is working hard off the pitch to try to improve his own game, and Dani Alves of Barcelona is a point of reference. Alves's sense of adventure at right-back is one that appeals to Walker, and he regularly watches clips of the Brazil international in action on his computer.
"I watch Dani Alves constantly on YouTube," said Walker. "It helps that he plays for Barcelona, but he is forever in the opponents' penalty box. It is fantastic how he gets forward, but also defends when he has to.
"He is a great player, so I make sure I study his game. If I do that for 10 minutes every other night, it's not going to do me any harm. I watch him to see what he's doing well, and I also look out for clips of Gary Neville. He didn't have that much pace, but his positional sense was so good he was very rarely beaten, and that's what I want to bring into my game as well. This is my first full season in the Premier League, so my career has only just started.
"You can't just rely on strength and speed because someone is going to outwit you. Not everyone who is good at football is quick and strong, so it's about football intelligence, too. If I can get my positioning right and keep going forward, hopefully I'll be the complete right-back."