Nietzsche isn't warning us against having beliefs—he's pointing to something subtler: the *certainty* with which we hold them becomes a wall against evidence. A liar might shift his story when caught, but a person convinced of his rightness simply interprets contradictions as proof he was misunderstood. Watch how someone defend a long-held political position: they don't usually change their mind when presented with contrary facts; instead, they reinterpret those facts to fit what they already believe. The danger isn't doubt—it's the smug confidence that closes the door to doubt entirely.