Yeah, I know... who'd have thought it!? Basically, even if you do happen to become really really successful, it still doesn't mean that your career will go on to prosper in the future... and unfortunately, the examples of some stars I have for you below only prove this to be true.
Robert Englund is also a man of one solitary role... but boy oh boy, what a role that is! Freddy Kruger became his biggest achievement as well as the role he appeared as more often than any other. At the end of the 80s, he was the most popular character and he portrayed Freddy from the years 1984 to 2003.
There wasn't actually any danger to his career, obviously, however, at the beginning of the '90s, his wife tragically died of cancer. After that, Moranis made the executive decision to leave the world of acting so he could focus on raising his children... which is pretty darn admirable if you ask me.