Repeated associations can become so entrenched that imagining a countercase feels difficult. That difficulty may be mistaken for logical impossibility.
Suppose a person has seen only colored objects and concludes: “Anything without color cannot exist.” Limited visual experience has been turned into a universal condition of being.
The decisive question is not how confident the speaker feels but what makes the unrestricted claim necessary. Treating a habit of perception as a universal proof is characteristic of illusory reasoning.