People in the 17th century believed in witches for three main reasons: 1. Superstition and a lack of scientific understanding led people to attribute unexplained events to supernatural causes like witchcraft. 2. Religious and cultural beliefs at the time taught that witches were real and that their powers posed a threat. 3. During times of hardship, a need for explanations and scapegoats emerged, and witches served as targets to blame for people's misfortunes.