It is possible that your ancestor was missed by the census taker, but make certain you have truly looked first, including a manual page by page search if necessary. It is possible too, that your ancestor lived somewhere else for a short time, perhaps even some place of which you are not aware. People do occasionally get overlooked by the census taker, especially if they are people who move around a lot in the first place or otherwise live a lifestyle that puts them at risk for being overlooked.