However, by the end of the series, we learn the devastating twist: the cancer goes into remission. The excuse evaporates. Walt could have stopped. He could have taken the money, hugged his family, and died a hero. But he didn't. He kept cooking.
Consider the pilot episode. Walt is given a terminal diagnosis. He has a choice: accept charity from his wealthy friends (Elliot and Gretchen Schwartz) or manufacture meth. He chooses the latter. The cancer becomes his alibi. He tells himself, "I am a dead man walking, so my morals no longer apply." why did walter white get cancer