Daily Chinese Idiom Guessing Game
Over time; as time passes; gradually.
经过了相当长的时间。
清·李汝珍《镜花缘》第十三回因置大缸一口，内中贮水，日日伏其中，习其水性，久而久之，竟能在水一日之久。”
If you practice daily,久而久之 you will become skilled.