One major sign of intelligence is listening to those who are greater experts than us. It is true that Albert Einstein smoked when he was a young man. A lot. It was widely believed that there was nothing wrong with it, and tobacco companies frequently and openly promoted it.
Albert Einstein's doctor told him that his heavy smoking was to blame for his declining lung capacity as he got older and advised him to quit. And he did it right away; he reportedly never lit up his pipe or smoked a cigarette again. Nevertheless, Einstein is frequently depicted holding a pipe in his mouth because he was fond of the practice and continued to smoke it even when he did not use tobacco.
Even if a doctor tells you that an unhealthy habit is harming your health, it is still stupid to keep it even after they tell you it's bad for your health. It's not stupid to have an unhealthy habit and keep it for a while without thinking about it. Einstein was by no means stupid — he immediately stopped when his doctor asked him to because he knew his doctor to be more knowledgeable than himself on the subject, and he trusted his judgment.