It is three years since Watford last played Crystal Palace in the FA Cup, Palace prevailing at Wembley in the 2016 semi-finals. It is a match that carries particularly strong memories for Adrian Mariappa; as a graduate of Watford’s youth system he was looking forward to facing his former club on the nation’s greatest stage, but what could have been one of the highlights of his career became one of its greatest disappointments.

“I travelled but I didn’t make the bench, and I was devastated,” he recalls. “Devastated. We played a league game during the week and I started that game. I came to Wembley, playing Watford, my hometown club, and when I found out I wasn’t involved at all, not even on the bench, it was gut-wrenching. I tried to keep a positive outlook for the guys who were playing, and it was a great day for the club, but it wasn’t a nice feeling.”

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Four months later he rejoined Watford after a four-year absence, apparently as low-cost squad padding, a free-transfer homegrown player to make up the numbers. During the first 30 league games of that campaign, three while still at Palace and the remainder in Hertfordshire, he did not spend a single minute on the pitch. The following April, amid a horrendous injury crisis, Walter Mazzarri was forced to give him a go, and Mariappa kept his place for the remainder of the season.

Mazzarri’s successor, Marco Silva, and the current manager, Javi Gracia, both doubted the defender, casting him to the sidelines before being won over. He has played 56 of 77 league games since April 2017, and is now 21st on the list of the club’s all-time appearance-makers with 309.

“There’s been moments that have been really tough in my career, when I’m not playing,” he says. “For a long time at Palace I was travelling to matches and I wasn’t making the bench, and I hardly played any league games. It does become tough mentally. But I don’t think I ever doubted myself or my ability. I just knew I had to get through this time and stick to the principles that have got me to this place. You skip forward to now, it’s justification to myself, I was doing the right things.

“Football’s an opinion-based sport and you can go from one manager who believes in you, believes in your ability and plays you every week, to another manager who might not think you’re for them, and through all that you need to have complete belief in yourself and try to do all the small one percents to improve. That’s what I believe. I’ll work on the little one percents to improve myself and make myself a better player, and the rest of it essentially isn’t in your hands.”

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It is a lesson Mariappa had to learn early. Having joined Watford as an eight-year-old he worked his way through the system until at 15 they decided not to offer him a scholarship, and for a while the dream seemed if not dead, then at least very distant.

“I was playing up with the under-17s when I got my decision that I wasn’t going to get a full scholarship. And the next day I was back playing in the under-15s. At the time that felt like my world had shattered. But the next day I made the decision that I would do everything I could, everything that was in my control to try to make it in football.

“I didn’t use it as an excuse, I used it as something to spur me on. They’re principles that have stuck with me, throughout my whole career. When I came here I was probably the sixth-choice centre-half, and I had to wait for a lot of injuries to get an opportunity. I’ve always tried to stick by what I know is the right thing to do – train hard, keep myself mentally at it, so when I get an opportunity I can take it.”

Facebook Twitter Pinterest Adrian Mariappa, here in action against Burnley, says: ‘I always enjoy the challenge of playing against someone who’s bigger than me.’ Photograph: Richard Heathcote/Getty Images

As a teenager Mariappa enrolled with an athletics club, missing summer holidays to work on improving his speed. “My sprint technique was terrible – quite flat-footed, I needed to learn to run on my toes,” he says. He was also shorter than most centre-backs, so he joined a basketball club to improve his jumping. “I moved to centre-half at a very young age and probably from the age of 14 onwards I was told, every single year, I was going to have to try to adapt my game to play right-back or midfield.

“But I knew my best position was centre-half and I used to work relentlessly on my jumping and my timing. My dad used to do loads of work in the garden with me. I always enjoy the challenge of playing against someone who’s bigger than me, and trying to prove that it doesn’t matter about my height [5ft 11in]. If I hadn’t worked on that, and I didn’t get my timing and my jumping right, I don’t even know what would have happened to be honest.”

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Now 32, he continues to work on those one percents. More recently, hoping for another small improvement, he adopted a vegan diet. “I did a bit of research and thought: ‘Let’s give it a go.’ I’ve never been one to follow a fad diet. A lot of people have said I’m just following a trend, but a year and a half later I’m still doing it. I wouldn’t say I’ll never go back to eating meat, but I can’t see myself going back to eating meat. It’s served me really well so far. I feel like I can recover quicker and obviously the older you get, the more important being able to recover is.”

He is in some ways an embodiment of the club he represents, not only because it is nearly a quarter of a century since he first joined – “I’ll never be able to get away from Watford. Whatever I’m doing I’ll always be part of this club” – but because Watford, like Mariappa, are smaller than many of their rivals, often unfancied, forced to work tirelessly on the one percents to remain competitive.

There are 31 English clubs, including every Premier League team except Bournemouth, who exceed Watford’s average attendance of 20,211 this season, yet Gracia’s side are eighth in the table and will reach another FA Cup semi-final should they beat Palace.

“I don’t think we’ve finished yet,” Mariappa says. “I don’t think the owners here will settle for complacency. They won’t let the players do it and the manager definitely won’t. A lot of people thought at this point in the season we would just down tools but we haven’t. Who knows where the club can go? One step at a time. We just want to finish the season well, and make another big step forward.”