Doubt is my key to success, says Schumi

BERLIN - Germany's seven-time Formula One champion Michael Schumacher admitted on Wednesday he had doubts ahead of his historic comeback but also that uncertainty was a secret to his success.

"I always had doubts in myself before, even in the good years," 41-year-old Schumacher, who returns after a three year hiatus at the season-opening Bahrain Grand Prix with Mercedes GP on Sunday, told Germany's Stern magazine.

"I think that this is part of the reason for my success - constantly looking for new areas where I can improve."