After we finished the hardest part, the rest of the project was smooth sailing.

가장 어려운 부분을 마친 후, 프로젝트의 나머지는 순조롭게 진행되었다.

I thought getting a promotion would be smooth sailing, but there were many challenges.

승진은 순조로울 줄 알았는데, 많은 어려움이 있었다.