Fernando Alonso believes Honda's inability to sustain its efforts each year from a solid foundation led to the failure of its partnership with McLaren.
The Japanese manufacturer which enjoyed great success in F1 in the 80s returned to the pinnacle of motorsport in 2015 with McLaren, in the second year of the sport's V6 hybrid era.
It's first year was marked by incessant reliability issues however which improved in 2016 although performance remained depressed. The introduction of a new power unit this year was met with even more reliability troubles which dogged the Woking-based outfit's campaign at the outset.
McLaren-Honda's form, or lack of, in pre-season testing, when everything is validated rather than trial and tested, put the writing on the wall, says Alonso.
"I think the biggest problems we faced in the last three years was winter testing, because we came to the next season, and we started from zero," said Alonso in Japan.
"So we had to improve things a lot, and Australia was a test, China was a test, Bahrain was a test, and we ended up with a package, a power unit, that we knew more or less how it works.
"That put you in a position and a hope that next year you will start there, and the gap is closer and closer. And it didn't happen.
"Every single season we had to change the philosophy of the engine, we had to change the turbine position, we changed different things that slowed us a little bit too much in terms of development."
Despite the turbulent period and the painful lack of results, Alonso claims he is proud of the work achieved by McLaren, and working with Honda has been a special experience.
"There are ups and down in all the teams," he said.
"The good thing is I think together with the Japanese mentality, no one gave up, they're still always working.
"We didn't deliver the results that everyone was hoping for, and that's a shame, we're sad for that.
"But we're still proud of the work that the team achieved with all the difficulties we found in winter testing. We tried to overcome all those problems in as short a period as possible.
"I will always still be proud of this project, even if the lack of results will say the opposite, and will be remembered as a bad timing, and frustrating timing, which it was, and it is now.
"I always loved Japan from the past, I have a samurai tattoo on my back, and to work in a Japanese organisation was quite intense, it was special, it was a different way of working."