Mauricio Pochettino said it is always a gamble to sign young players like Dele Alli from lower-league clubs, and that Tottenham got lucky with Gareth Bale after nearly letting him leave before he developed into a world-class talent.
Spurs bought players Aaron Lennon, Tom Huddlestone, Danny Rose and Kyle Walker from clubs outside the Premier League when they were teenagers, and they profited in particular when they took a 17-year-old Bale from Southampton and eventually sold him to Real Madrid in 2013 for a then £85 million world-record fee.
They got another bargain when they recruited Alli from MK Dons for just £5m, but Pochettino explained why they have not made more similar signings since, arguing that even Bale's achievements in north London owed much to fortune.
"Remember with Bale, after three years he started to be a success but they believed they signed a left-back and today he's the opposite," Pochettino said. "That was a little bit lucky, to be honest.
"When they told me about all that happened, they wanted to [get rid of him]. You know better than me the history. In football, sometimes something appears and you say [thank you God] and it's so lucky. Yes or no? That's the truth! Come on, after four years we know each other and we need to be honest.
"It's difficult to find players like Dele, but sure there are talents in the Championship, League One and below. There's always talented players, but then it's about getting lucky with this type of player.
"You need some people like us, when Dele came, to provide a platform. Of course, all the credit is for the player but it's not the same if Dele Alli arrived from Milton Keynes to another club. Today it would be different -- maybe better, maybe not, but different.
"That's why it's so important the players have luck with their interest from some clubs. Interest from Tottenham is a massive thing because Tottenham have a very good platform to help the younger players improve."
Pochettino continued: "It's like when people ask me about teams in Spain and Italy who have a different approach in the market. Yes, many players are a success but many players fail.
"If every season you sign 10 young players, it's a gamble. You take the risk. But it's normal that out of 10, five are good, maybe one is excellent and four disappear.
"People say 'oh it's very nice how they signed, very good, because they signed Bale' but many players fail. It's about percentage.
"You're always going to remember Bale or Modric -- the good ones. But if we find the list, many players failed here in the previous seasons, that we and other people signed."