An idiom meaning that as soon as one difficulty is over, another one appears; similar to 'out of the frying pan into the fire' or 'one thing after another.'
台風が通り過ぎたと思ったら、今度は大雨で一難去ってまた一難だ。
Just when we thought the typhoon had passed, heavy rain hit us — one problem after another.
プロジェクトは一難去ってまた一難で、次々に問題が出てくる。
The project is one setback after another; problems keep coming up.
子育ては喜びも多いが、一難去ってまた一難の連続だ。
Raising children brings much joy, but it's a continuous series of one challenge after another.