Honda's terrible three-year spell with McLaren helped the Japanese manufacturer learn with it had "lost" being away from Formula 1.
After leaving F1 before the 2009 season Honda was tempted back as McLaren's exclusive engine supplier for 2015, targeting a revival of its ultra-successful partnership from 1988-1992.
But McLaren-Honda failed to score a podium together in three seasons hit by poor performance and reliability and the two parties divorced last year.
Honda is now preparing to supply engines to Red Bull in 2019, as well as '18 partner Toro Rosso.
"The first three years with McLaren after the return for Honda were very, very important because it was three years of learning what we had lost in the gap between last time and returning to F1," said Masashi Yamamoto, Honda's motorsport boss.
"We're very appreciative of those three years.
"Then when we joined with Toro Rosso, from the beginning we realised it was a beautiful collaboration, and we were ready for the next step: to win races.
"To win races, we decided that getting together with Red Bull is the right choice."
Honda has been keen to highlight its "respect" for Red Bull in what Yamamoto calls "a very fair relationship".
It has benefited from access to Red Bull Technologies facilities already thanks to the Toro Rosso deal, particularly the use of rig-testing for its engine.
Management changes have also helped Honda apply greater focus to its research and development work in Sakura.
Those factors have all combined to help Honda make a significant step in performance this season, which has been noticed by McLaren.
"They are intelligent people who are working very hard," said McLaren F1 CEO Zak Brown when asked by Autosport about Honda's improvement.
"They've probably learned from the past three years. We collaborated with them a lot, gave them our views on areas we thought would help in their development.
"I don't know what they've done in the off-season [but] good companies, good people learn from difficult times.
"I think they've taken a step forward and maybe we contributed to pointing out areas they could get stronger and embrace, and that's exactly what they've done."
While Honda has grown in stature since the split, McLaren's deficiencies with its car design have been exposed by Renault power.
The team is struggling compared to Red Bull and the works Renault outfit, with an aerodynamic problem that McLaren has been unable to identify in the windtunnel.
Asked if he was happy to see McLaren struggling after an unhappy three years in which Honda received criticism from the team, Yamamoto said: "We're not happy there is a struggle.
"In racing it is very difficult to have the entire package: the chassis, the engine, the running of the team. It's not an easy task.
"For us it's very important to see how Renault, how McLaren, deal with all that.
"We've been learning a lot from our experience and other teams' experiences."