Excerpt from "In All Your Ways" by Rabbi Yaakov Meir Shechter:
I heard a story about a great Torah scholar of the previous generation who was known for his remarkable diligence in study; he finished the entire Talmud many times. At the completion of one such cycle, he made an especially beautiful banquet. Why was this occasion so special, his family asked him? Hadn't he finished the Talmud many times before? He explained that this time was especially dear to him because he had done it all in his spare time. He always carried a small Gemara with him wherever he went, and would study from it during those spare moments that other people ignore: traveling, eating or waiting in line. This accomplishment made him extremely happy and so he made a special banquet. There are some people whose lives are so preoccupied by different projects that the only way they can even finish a book is by snatching up these free minutes. It only requires alertness and enthusiasm.