Jurgen Klopp knows Liverpool's latest centurion better than most.
The man who gave Trent Alexander-Arnold his Premier League debut in December 2016 - a 3-0 win over Middlesbrough - named him again on Saturday for top-flight appearance number 100.
Under Klopp, Alexander-Arnold has developed from an academy up-and-comer into a Liverpool favourite, then an England international, a Champions League winner and, in June, a Premier League champion.
As the right-back played in the league for the 100th time against West Ham, under the floodlights at an empty Anfield, a 2-1 home win sent the Reds top of the pile once more.
Klopp was asked about Alexander-Arnold's milestone before the victory that saw Merseyside rivals Everton usurped again - at least until Sunday.
"It's a great number," the manager said. "It's an interesting journey. He came in with a super basis as a player, as a person, and used it to make big, big development steps.
"I heard about [the milestone], and when you see pictures from his pretty much first game - really, the boy who came and the man he is now, even though he's a young man - the difference couldn't be bigger.
"Of course, when you look at his age, there is a lot of space for improvement, just time-wise already, and he will use that.
"He will become even a better person - maybe that's difficult, but more a personality and all these kind of things.
"It's really nice to be a part of this journey, to be honest, because everybody dreams of something like that and then, when you are part of it, that makes it pretty special."
THE FULL-BACK'S FIRSTS
After his debut, Alexander-Arnold was installed in the Liverpool line-up as soon as January 2017, starting against rivals Manchester United in a 1-1 draw.
He played the full 90 minutes and created his first Premier League chance, although that was one of only two starts before the end of the campaign and he was hooked at half-time against Stoke City in the other.
Outings were more steady the following year and Alexander-Arnold's breakthrough top-flight goal arrived against Swansea City in a 5-0 demolition in December 2017.
He ended the 2017-18 season with just one goal and one assist, which came when Mohamed Salah nodded in his cross against Bournemouth in April 2018.
The next campaign was far more impressive.
THE STANDOUT STATS
Alexander-Arnold was one of Liverpool's key performers as they took the Premier League title race to the wire in 2018-19. With a hat-trick of assists against Watford in February 2019, still just 20, he became the youngest player in the competition's history to create three goals in the same game.
He then reached double-figures for assists with two at Newcastle United in May, making Liverpool the first Premier League team to have two defenders supply 10 or more goals. While the right-back ended the season on 12 assists, left-back Andy Robertson had 11.
That form continued into the next season, too, and in August he was just the eighth player in Premier League history - and first since Mesut Ozil in 2015 - to have an assist in five straight games.
Even after that run ended, Alexander-Arnold had 10 assists again by January. Only Cesc Fabregas had reached double-figures in two separate seasons by the age of 21.
Sure enough, in April, he became the youngest player to 25 Premier League assists - at 21 years and 140 days - and the records continued after Liverpool's title triumph as he surpassed his own benchmark for the most assists by a defender, registering 13 last term as Robertson managed 12.
At 22 years and 24 days on Saturday, Alexander-Arnold became the 12th-youngest player to reach 100 league appearances for the Reds and the youngest since Steven Gerrard in 2002.
THE REDS' RELIANCE
There is no doubt Liverpool now depend hugely on the 22-year-old. Against West Ham, Alexander-Arnold played more crosses (eight) than any team-mate, while only captain Jordan Henderson attempted more passes (113) or had more touches (141).
Although his one shot and one created chance did not add to his totals, the defender has six goals and 27 assists in his Premier League career.
The Reds have won 77 of the 100 games Alexander-Arnold has played in, while their win rate in the 44 fixtures he has missed in that time stands at a rather more ordinary 54.5 per cent.
Unsurprisingly therefore, Liverpool collect 2.5 points with Alexander-Arnold in the side, compared to 2.0 without. They also score more often, 2.3 goals per game versus 2.0.
Klopp and his side can thus take comfort knowing Alexander-Arnold does not look like going anywhere.