Carlos Sainz knows the process of moving Williams up the Formula 1 grid will take some time, but the 30-year-old Spaniard said his motivation to do so is "unbelievable."
Sainz jumped in his Williams car for end-of-season testing on Tuesday, and posted the second-fastest time behind Charles Leclerc as teams tinkered with setups and run plans.
Sainz and Leclerc have been teammates for the past four years at Ferrari, where they helped claim second place in this year's constructors standings.
Podiums and team successes of that nature are still a long way off for Williams, but Sainz said that is of no concern to him as he embarks on his biggest project after racing for Ferrari (2021-24) and McLaren (2019-20).
"I'm not worried about that," Sainz told DAZN Spain, per f1.com. "I've got that. I've done that with Ferrari."
While Ferrari was overtaking Red Bull and battling McLaren to end the season in Abu Dhabi, Williams finished ninth out of 10 teams in the constructors standings.
While 17 points left the team 29 behind RB Honda for eighth place, Williams has been making steady strides since investment firm Dorilton Capital bought the team in 2020.
The highly respected James Vowles brought in Sainz, who was replaced at Ferrari by seven-time world champion Lewis Hamilton, to provide a veteran driver pairing alongside Alex Albon. The trio are part of a comprehensive plan to return Williams to its glory days.
"Honestly, people won't believe it and can't imagine how much I'm looking forward to what's to come," Sainz said.
"It may seem strange to people but it's a project that motivates me a lot. It's in my mind to be able to help a legendary team like Williams in F1 to become a top team again. Being part of that motivates me a lot."
Sainz is a four-time winner in Formula 1, with his most recent victory coming at the Mexico Grand Prix in October.
It was his second win this season, following his March victory in Australia. He has known he would be out of a ride with Ferrari since the Hamilton news broke in February, and Sainz took his time before signing with Williams five months later.
The split with Ferrari was amicable, including the team releasing him early to participate in the end-of-season testing, but Sainz admitted it was a challenge racing the full season knowing it would be his last with the legendary Italian outfit.
"I think the way to face a year like this is never ideal," he explained. "All the great years of the best sportsmen in history come with a 100 per cent team, a project for the future and everyone pushing in the same direction.
"And yes, I have noticed that Ferrari has supported me at all times and all season long. But whether you like it or not, when you know you're leaving at the end of the year, it's complicated to manage.
"We have all managed to stay out of it and keep giving it our all. The end of the season has been very nice and a sign of strength that I think will help me in my next projects."