Mertesacker says a strong league finish and an FA Cup win at Wembley, which would end a nine-year wait for a trophy, would represent a positive season.
"We have struggled heavily with a couple of injuries, but we have regrouped very well and how we managed the situation was maybe more important than last year, so securing Champions League football was another test for us," said the defender.
"However, everyone wanted us to get further up, especially the fans, and we were top of the table for a long time. Everyone dreamed about the title, but it takes more than staying top until the winter period.
"We could not afford those (losses) in big games against big teams, so we did not deserve to be in the first three. That is something we have to manage much better next year.
"Everyone questioned our qualities, but how we came back as a team, that makes us stronger for the future.
"We are in a cup final and it is important to secure Champions League football, so these are good targets to go for.
"We are happy to have a lot of players back. The squad is getting stronger and stronger."
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