Catechism of the Catholic Church §1739 — excerpt
Freedom and sin. Man's freedom is limited and fallible. In fact, man failed. He freely sinned. By refusing God's plan of love, he deceived himself and became a slave to sin.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.