Mercedes was paranoid throughout 2014

Although Lewis Hamilton and Nico Rosberg won 16 out of 19 grands prix this year, Wolff says he was always paranoid that the opposition would close his team down and knock them off the top spot.

"I am such a pessimistic person by nature," Wolff told AUTOSPORT. "It was not until the flight back from Suzuka to Europe, obviously with the black cloud of Jules's [Bianchi] accident there, that I realised for the first time we have a dominant package - and we might be able to win.

"I didn't have those thoughts at all through the season. I never believed that it was an easy pass - in fact it was the contrary."

Wolff believes fears about what other teams could do were immediately fuelled by Red Bull's recovery from a disastrous pre-season testing programme to take a podium finish on the road with Daniel Ricciardo in the Australian GP season-opener.

"Everything we saw since the beginning of the season was not indication enough that our package would be good enough," he explained.

"When we came into Melbourne, Ricciardo finished second before it was taken away - from barely any testing.

"So that was a bit of a reminder that we should not be complacent. That is why we went from race to race, trying to improve performance and, if you look at the season, it was the first time that the team ever increased the gap throughout the year instead of falling back.

"Even in 2009, it went down. Last year we were really doing well until the summer break and then after the summer break we just lost out to the nine victories of Sebastian Vettel. And this year the opposite happened."

Wolff blames his own personality for never feeling comfortable about the lead that Mercedes had, but thinks that trait is also a strength.

"In the past in my own jobs, I never felt comfortable with anything until it was done," he said. "And it is not because I said that I should never be comfortable, it is just the way I am calibrated. I don't believe it is done until it is done.

"It certainly doesn't make my life easier. It gives one miserable day after another, but it is a strength in always expecting the worst.

"Because you are managing your own expectations in yourself, and keep yourself pushing hard because you do not believe it is ever good enough."