London - Son Heung-min has every reason to be constantly smiling, and Tottenham have many reasons to be thankful.
For a footballer so understated, so seemingly undemanding, the forward has become indispensable for Tottenham.
Borussia Dortmund was reminded of that in the Champions League on Wednesday night, when Son scored the opener to spark a 3-0 victory in the last-16 first leg. It was Son's ninth goal in 11 games against Dortmund, including his time in Germany playing for Hamburg and Bayer Leverkusen.
It was also the South Korean's 11th goal in his last 12 games, as he once again took up the scoring role in the absence of striker Harry Kane, who is still recovering from injury. With this commanding lead - secured by late goals from Jan Vertonghen and Fernando Llorente - Tottenham is dispelling suggestions it is overly reliant on Kane.
It's been a remarkable contribution for Son, considering he started the season at the Asian Games and took a couple of weeks out in January to go to the Asian Cup with South Korea.
"Son is a player that of course has a lot of quality and is a very talented player," Tottenham manager Mauricio Pochettino said. "But he is always available to learn, improve and listen to what you expect from him. He is capable of adapting the quality in different situations."
He proved that right at the start of the second half after Tottenham had been run ragged in the opening 45 minutes and was on the back foot after an error-strewn performance.
In the dressing room, Pochettino got the video clips out during the break.
"We showed a few actions defensively and positions in the offensive situations," Pochettino said.
Within two minutes of the restart, Tottenham was in front after Dortmund left Son unmarked to volley into the net to make it four goals in as many games since returning from the Asian Cup.
"I just had to touch the ball," Son said, praising Jan Vertonghen, who provided the cross.
Son celebrated with a trademark Tottenham handshake, but went over to Serge Aurier rather than Vertonghen.
"I feel sorry," Son laughed after the game alongside Vertonghen, "because I didn't run to him and I ran to the other side."
Vertonghen got his own chance to celebrate as Tottenham scored two late goals inside three minutes.
Vertonghen raced into the penalty area and arrived at the back post to volley in Aurier's cross in the 83rd minute.
"Technically he's just unbelievable," Son said of Vertonghen, who was playing at left wingback rather than in central defense. "He can play every position. He deserves a goal and an assist."
With Dortmund struggling, Llorente scored the third in the 86th when he got a slight touch with his head to turn in Christian Eriksen's corner.
It was a night to forget for United States international Christian Pulisic, who will be playing in London for Chelsea next season, and Jadon Sancho, the 18-year-old former Manchester City attacker who faded in the second half.
"We lost focus," Sancho said. "Son is a good player but hopefully we can handle him better in the second leg."
It is the third setback in a week for Dortmund, which was knocked out of the German Cup by Werder Bremen and then drew with Hoffenheim in the league.
"There are periods of a season when things aren't top, top, top," Dortmund manager Lucien Favre said. "We need to analyse and work hard to avoid and correct these errors."
But Dortmund has a five-point lead in the Bundesliga over Bayern Munich, while Tottenham is five points off the pace in the Premier League in third. This is first time the London team has made the knockout phase in Europe's elite competition in successive seasons. Unlike Dortmund, Tottenham has never lifted the European Cup.
In the night's other game, Real Madrid scored a later winner to beat Ajax 2-1 in Amsterdam.