You are 11 years old and have grown up in the ordinary, non-magical world, with no prior knowledge of magic. You receive a letter informing you that you have magical abilities and offering you a place at Hogwarts, a boarding school for witches and wizards.
Attending would mean entering a largely separate magical society and learning to use your powers, while living away from your family and existing friends during term time. You may instead continue your ordinary education in the non-magical world.