Lewis Hamilton says he has been at his best this season, but his McLaren team have not done a good enough job to win the World Championship this season.
Hamilton, who retired from the lead in Abu Dhabi, has suffered a series of mechanical failures, pit stop errors and team mistakes this season.
"This year has not been the easiest as I've been at my best," said Hamilton.
"We have had a lot of failures in the last four or five races, so reliability has been a big issue for us."
Hamilton, who is joining Mercedes on a three-year contract next season, added: "We've had too many problems to have been able to win. We have not done a good enough job to have been able to win the championship.
"I have no doubts the team can fix it. We just need to keep our heads up and keep looking forward."
Hamilton began the season with three successive third-place finishes, but he could have challenged for victory in Malaysia had the team not struggled with fitting the tyres in two separate pit stops.
The 2008 world champion finished down in eighth in Bahrain after another pit stop error, while in Spain the team didn't put enough fuel in his car for qualifying.
As a result, he was forced to stop on track after securing pole and later demoted to the back of the grid - like Sebastian Vettel was for Abu Dhabi.
There was more pit stop pain in Valencia before he retired after being hit by Pastor Maldonado. And in Germany he retired with rear floor damage.
The Brit was taken out at the first corner in Belgium by Romain Grosjean and a broken gearbox saw him retire in Singapore from the lead.
In Abu Dhabi, he was quick all weekend and comfortably leading the race before a fuel pump problem forced him out.
Despite the disappointments, Hamilton remains upbeat for the two remaining races - at the new circuit in Austin, United States, and the finale at Interlagos in Brazil.
"We hadn't brought any upgrades [to Abu Dhabi]," he added. "We have some coming for the next race.
"I really hope the car performs as well in the next two races so we can get back up the front and maybe finish a race up at the front for the last time. I'm really happy with the job I did. I couldn't have done any more."
McLaren boss Martin Whitmarsh added: "This year, we've had a quick car and haven't got all the points we should have.
"You have years when it seems easy and years when it's hard work. This is one of those hard work years.
"We're obviously a little bit disappointed right now, but we'll look forward with a quick car and two motivated drivers and go out and try to win those two races."