Red Bull team principal Christian Horner admits never in his wildest dreams did he expect Sebastian Vettel to produce four titles in a row.
Vettel joined greats like Michael Schumacher and Juan Manuel Fangio in the record books in Indian on Sunday as he joined the elite club of drivers to have won four consecutive World Championships.
"It was very clear very early on that Sebastian is an exceptionally talented driver," he told PlanetF1's Chetan Narula in an exclusive interview. "But I don't think any of us could have dreamed that he will have the success rate that he has enjoyed. He has developed, matured and improved as a driver, and he has shown us that year upon year. And now, he is performing at a level which continues to surprise us."
Asked to pinpoint the reason for his success, Horner said: "It is his mental strength which is a key point, I think. Whether that is in qualifying when he needs to deliver a lap, or whether when he needs to deliver in a race. Whether that is nursing tyres or producing fast times by extracting everything out of them, he has the ability to react and deliver at different pressure points during a grand prix weekend."
Vettel has consistently outperformed his more experienced team-mate Mark Webber the last couple of years and Horner believes it shows just how good the German is instead of how poor Webber is.
"Mark is a very strong driver. Prior to Sebastian joining the team, Mark had destroyed every team-mate he had gone up against. And then for Sebastian to come in and beat Mark just indicates the level at which Sebastian is operating.
"It is very easy to underestimate Mark Webber. He has driven some great races for us, but it puts into context the level at which Sebastian has been performing and Mark himself would be the first to recognise that."
When asked again about comparing Vettel and Alonso: Horner replied: "That is a very difficult one to answer. Fernando Alonso rarely gets compared with his team-mate and you can argue the same for Lewis Hamilton, irrespective of the team.
"Mark is a very strong driver and what Sebastian has produced is extra-ordinary. We are not finishing first and second in every race. He has quite often won in a car that hasn't been the best on the grid, particularly last year (2012). Or even some races this year, the Nurburgring for instance. The Lotus on that day was the quicker car!"
Full Q&A with Christian Horner