As I understand it, Li Xiannian was the first to coin this term. It emphasizes the spirit of experimentation. Everything must first be tested; if successful, the policy may be extended, and if not, we can turn back.
「摸著石頭過河」據我所知最早是李先念講的，卻以此強調的是務實的實驗精神，一切通過實踐，成功就推廣，不成功就回頭。