A colloquial expression meaning 'that's not going to happen' or 'it won't be that easy' — used to reject an expectation or to say plans won't go as hoped.
もう全部片付けたって？そうはいかないよ、まだ仕事が残っている。
You finished everything already? That's not going to happen — there's still work left.
彼が簡単に許してくれると思ったら、そうはいかないだろう。
If you think he'll forgive easily, that's not going to be the case.
計画通りに進むと思ったが、現実はそうはいかない。
I thought it would go according to plan, but reality isn't like that.