Explanation
Expresses the idea 'it's not that it's impossible' or 'it's not that I can't'.
Formation
Verb-ないform + なくはない, い-Adjective－い + くはない, な-Adjective + ではなくはない, Noun + ではなくはない
Detailed explanation
The ～なくはない grammar point implies that while something may not be your first choice or not guaranteed, it's not outright impossible. Translates to 'It's not that it's impossible,' 'It's not that I don't/can't ~.'
Examples
Sore o oeru no wa muzukashiku naku wa nai.
It's not that it's impossible to finish it.
Kare ni hanasu no wa kowaku naku wa nai.
It's not that I'm entirely unafraid to talk to him.
Eiga o mi ni iku jikan ga naku wa nai.
It's not that I don't have time to go see a movie.
Nihongo de kouen suru no wa muzukashiku naku wa nai.
It's not impossible to give a lecture in Japanese, but it won't be easy.
Practice
Grammar content sourced from hanabira.org.