Glioblastoma is a highly malignant brain tumor with a dismal prognosis that requires multidisciplinary treatment, emphasizing 'maximal safe resection' during surgery. Neurosurgeons often rely on empirical knowledge, which suggests that removing only contrast-enhancing lesions should not cause new neurological deficits. However, we encountered a case in which this assumption did not hold true. A 60-year-old, right-handed man presented with declining frontal lobe function and a large mass involving the bilateral anterior cingulate gyrus (ACG) and left superior frontal gyrus (SFG). After initial removal of the left SFG tumor, the patient showed no new deficits. The pathological diagnosis confirmed glioblastoma, IDH-wildtype. A second surgery was performed to resect the remaining contrast-enhancing lesions involving the bilateral dorsal anterior cingulate cortex (dACC), via the initial surgical corridor. Postoperatively, the patient developed persistent abulia. This case highlights a critical exception to prevailing surgical dogma. Although the resection targeted only contrast-enhancing tissue, the involvement of the bilateral dACC, a key node of the salience network, likely led to severe cognitive and motivational dysfunction. Greater attention to functional neuroanatomy may be necessary to optimize outcomes in complex glioblastoma cases, even within contrast-enhancing tumor regions.