Daniel Ricciardo says leaving Renault to join McLaren next season was "by no means an easy decision".
The Australian was part of a series of driver changes for 2021, triggered by Ferrari's move not to retain Sebastian Vettel at the end of this season.
Ricciardo told the F1 podcast that his move was "not as clear" as his decision to leave Red Bull for Renault in 2018.
"Without any races, you have to believe. It's what pitch excites you more than the other," Ricciardo said.
The 30-year-old, who will replace Carlos Sainz at McLaren next year following the Spaniard's move to Ferrari, said he had been convinced by the progress McLaren made in overtaking Renault to claim fourth in the championship last season, and by their decision to switch engines to Mercedes for 2021. Renault, by contrast, had a disappointing year.
"Last year is our best reference," Ricciardo said. "They were the team that made the most noise. they made the biggest step out of all so that was encouraging. That's all you can base it off and then the pitch for the future. They are switching power-units. It was by no means an easy decision."
He said there was no single deciding factor and that the situation was "different" to when he decided to leave Red Bull at the end of 2018.
"That had run its course for me," he said. "I needed a change. This was not as clear. We didn't achieve what we wanted last year. I don't know. It was by no means an easy one and time will tell."
Getting back to racing
Ricciardo took part in a two-day test with Renault this week as the team prepared for the start of the season next month.
Drivers and teams have not operated their cars since the end of pre-season testing in February.
"It was good to get back into it," he said. "The first few laps felt a little foreign but it's like all things when you have been doing something pretty much your whole life, it doesn't take long until you remember the feeling and it all feels very normal very quickly."
Teams are operating using social distancing where possible and protective equipment where not.
Ricciardo said: "It was certainly different. Our debriefs were happening over video calls. Most of us were sitting in the same area but at distance so we're all doing our debrief through video meetings.
"Everyone has a mask on in the garage. There is just a little more awareness of personal space. Whenever there's a change it takes a bit of time to adapt but in time we do adapt."