Small issues can be forgotten when it compares to the overall interest in a story, however i think the reason why its good to correct oneself is because those errors take away from the reading experience.. and in the end youre cheating yourself and the readers because its a distraction, and when a reader is distracted you dont quite get the credit you deserve.

Generally I dont think its a major issue when I'm reading a story But it /can/ be an issue when there are enough mistakes that one can't entirely focus on the story he/she is reading.