Valtteri Bottas believes that if Williams is to return to the winner's circle it needs to learn from its mishaps and failures, and raise its game in all areas.
The Finn concluded his 2015 campaign fifth in the driver's standings, 15 points in front of his team mate Felipe Massa, achieving his best result of the year in Canada and Mexico where he scored on both occasions a third place podium finish.
Williams looked set to challenge Ferrari for a runner-up spot this season behind the untouchable Mercedes Silver Arrows of Hamilton and Rosberg.
But the British team's progress stalled in the later part of the year, and with it Bottas' competitive edge decreased. A decline partly pinned on Williams focusing its efforts on next season's car.
"There were lots of good moments, like a couple of podiums and successful races for us," Bottas said.
"But there were a lot of disappointments too, that we need to learn from, like I said before, because this is not the best we can do – we can do much better like this as a team.
"We have to remember the good moments more, of course, but what is the main thing is to learn from the disappointing moments."
At times, Williams appeared relatively weak in the pit stop department, but Bottas believes improvement must be sought in all departments if the Grove outfit it is to become a viable race winner.
"If we want to win we have to raise our game in all areas. For the last race of the year, the pace wasn’t there, and we need to make big gains over the winter if we want to fight with Ferrari and Mercedes again. And we also need to minimise the number of mistakes - that’s a fact."
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