Mark Webber admits he has struggled for motivation in recent years but still feels he may be leaving a year "too soon."
The Aussie announced earlier this year that he would walk away from F1 at the end of this season, his 12th in the sport.
Speaking about his reasons for leaving, Webber confessed to F1 Racing magazine that his motivation had been waning over the last few years.
"I've been on the edge with F1, motivation-wise, for the past couple of years," he said in an exclusive interview with the magazine.
"You have to be driven. You turn yourself around each winter and the fire in the belly is not quite what it was when you were 24.
"I remember hearing something about sportsmen and women years ago. They were saying that as long as they could keep their motivation, they would keep going.
"I could never work out what that meant. How could you lose your motivation? But questions keep coming to me more and more often that were never there in the past.
"It's not about driving or racing, it's about keeping my own F1 programme going for 11 months of the year. And it's just got to the point where it's like, well, I've achieved a lot of things."
The 37-year-old, though, reckons he may be leaving a year too soon but given the massive changes the sport will undergo next season, he says the time is still right.
He added: "I still enjoy being belted in the car and driving down the pit lane, which is a bit disappointing, but I've spoken to some really good sportsmen and women who have been at the crossroads where making the call was not easy and they messed it up.
"I'm probably leaving F1 a year too soon but with the [regulation] changes next season [the introduction of turbo engines with a fuel limit] and the opportunity to join Porsche, it's the best move for me."