Why did Descartes think that impulsively accepting beliefs causes errors?

René Descartes argued that impulsively accepting beliefs leads to error because human knowledge is often derived from sources that are inherently fallible or subject to deception. In his methodic doubt, he systematically set aside any belief that could be doubted, identifying several key reasons why uncritical acceptance is dangerous:12

• Unreliable Authorities: Knowledge based on tradition is dubitable because authorities frequently disagree with one another.12
• Sensory Deception: Empirical knowledge is untrustworthy because sensory experience can be misleading—such as when a distant object appears different than it is upon closer inspection.23
• The Problem of Dreams: One cannot always distinguish between being awake and dreaming, meaning beliefs about the immediate world may be mistaken.23
• Fallibility of Reason: Even simple mathematical or logical truths can be doubted if one assumes the possibility of a powerful, deceiving entity—such as an "evil genius"—that could manipulate human perception to ensure we err even in our most basic calculations.123

By rejecting these uncertain beliefs, Descartes sought to establish a foundation for knowledge based only on ideas that are clear and distinct, which he believed could not be doubted.23