Pascal Wehrlein says Sauber's performance deficit in 2017 meant his best drives, mainly achieved in the second half of the season, went unnoticed.
The German driver saved his team from a mortifying zero score in the Constructors'' standings thanks to his top-ten performances in Spain and Azerbaijan.
Sauber's management was ungrateful however, rejecting Wehrlein for 2018 when it decided to keep Marcus Ericsson alongside rookie and Ferrari protégé Charles Leclerc.
"In terms of result, [Barcelona] was the best race of the year but probably in the second half of the season I had better races, but you couldn't see it," said Wehrlein.
"Even if we had a good race in the second half of the season, you couldn't see it because the gap was just too big - for example, in Suzuka, I was lapped by the second-last guys.
"I'm quite happy in the end with five points. Not all of the races have been good as I wished but I think in general we did what we could do."
At just 23, Wehrlein, who remains under contract with Mercedes, isn't discarding a return to F1 in the future. But in the short-term, a return to the competitive DTM series appears likely in 2018.
"Definitely I was always giving my best, and I think that's the most important thing that you can say about yourself," he added.
"When an opportunity was there, we took it. With more experience you think 'ah, one or two races ago I was doing this direction with the set-up, now I know this was worse I should have gone in this direction', and you always learn something."
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