Daily Chinese Idiom Guessing Game
Year after year; repeatedly over many years.
一年又一年。比喻日子久，时间长。也形容光阴白白地过去。
清·李汝珍《镜花缘》第二回每逢闲暇，无非敲枰相聚。日复一日，年复一年，也不知人间岁月几何。”
He has been working on this project year after year without giving up.