There is a famous story about the Chofetz Chaim who was ready to move to Eretz Yisrael. He gave his goodbye sermon to his community in Radin on the Shabbos before his planned departure. Afterwards, a simple man came over to him and asked, “Why didn’t you say אם ירצה השם (G-d willing)?”
That Motzei Shabbos, the Chofetz Chaim’s wife suddenly became ill and the Chofetz Chaim never ended up going to Eretz Yisrael.
How important it is, when making plans, to always say אם ירצה השם