Former world champion Niki Lauda believes Michael Schumacher is back to race again because he regrets retiring from Formula One racing at the end of the 2006 season.
Schumacher is returning to F1 racing at this month's European Grand Prix, where he will replace the injured Felipe Massa at Ferrari.
Lauda says the seven-time champion is returning as he still has the competition bug, and he says the most successful F1 driver regretted quitting the sport.
"He was never able to detox himself of the racing bug, as we have seen with his on-track motorcycle activities. In my opinion he retired at the end of the 2006 season because he couldn't see a real challenge - and probably he regretted his decision," Lauda said.
"Now he's got the unique chance to step in for the injured Massa to help his former team, and to find out for himself how competitive he still is. This is something that would also interest me, because this hunger for competition - for the adrenalin rush - never dies. It's in our DNA.
"And the situation as it is now at Ferrari, with a recovering Massa and an available cockpit, gives him the chance to explore how far he's off the top. That is a question that always puzzles a top driver like he was."
Lauda, who also made a sensational comeback from retirement in the 1980s and went on to win the world title again, reckons Schumacher is treating his return as an experiment.
"I actually won the second race back after my retirement, but Michael is not racing for any championship. I came back because I wanted to win, if my comeback was successful. For Michael it's nothing more than an interesting experiment.