naive assumption

Translations
наивное предположение
It was a naive assumption to think that everyone would agree with the plan.
Это было наивное предположение думать, что все согласятся с планом.
Definitions
A naive assumption is a belief or idea that is overly simplistic or lacks critical analysis, often based on an incomplete understanding of a situation or subject. It typically disregards complexities and nuances, leading to potentially flawed conclusions.