In his book, the Dialogue, Galileo advanced the argument in 1632 that the earth was not the centre of the universe, and that the earth revolves around the sun. This idea of a heliocentric solar system was so controversial that the Catholic Church classified it as heresy, and the book was banned. Eventually, when it became common knowledge that the Earth was not the centre of the universe the Church lifted the ban on Galileo's Dialogue in 1822, but without a public apology to him. Mankind misunderstood the cosmos due to a lack of knowledge, and this was not the only time we goofed.
Throughout history, there have been numerous other examples of big errors made by mankind, many of which persisted for centuries before being corrected. Here are a few examples: