If you smoke a cigarette once, you've simply made a bad choice. But if you're a chronic smoker, you've been smoking for a long time and will have a hard time stopping.
The word chronic is used to describe things that occur over a long period of time and, in fact, comes from the Greek word for time, khronos. If you have chronic asthma, it is a recurring health issue for you. No one likes a chronic liar! A problem that cannot be solved can also be called chronic - think of the chronic food shortages in certain parts of the world.