Honda opted to change its F1 engine concept over the winter, but ran out of time to be sufficiently prepared for the season.

It suffered a series of failures and, in a bid to save its relationship with McLaren, aggressively introduced performance developments at the expense of reliability.

While McLaren decided to switch to Renault engines for 2018, by the end of the year, it was able to fight consistently for points with Honda.

"Our performance improvement level is something to be proud of," Hasegawa told Motorsport.com before the news broke that he would leave his role as head of Honda's F1 project at the end of the year and instead work on road car projects.

"Our competition level was lower than expected so we needed to update more often. We needed to sacrifice time checking reliability to get the updates to the track. It was strategic.

"We are confident we can confirm the reliability, This is just a time issue. We prioritised the performance update over checking reliability."

Hasegawa admitted Honda's reliability in 2017 was "not acceptable" and is an area it needs to focus on over the winter.

Honda struggled with correlation in the first half of the season, with reliability progress achieved on the dynos not being replicated on track.

"It's very bad that we have had failures on the track and on the dyno," he said.

"Reliability, we had a clear target, which is we have to be able to complete five races with one engine but we haven't achieved that. It's a clear point. We are very disappointed."