The malignant brain tumour disease condenses much of the anguish of cancer diseases. The brain is a vital and delicate organ, and the prognosis is generally unfavourable. The patient is exposed and has to rely on cognitive manoeuvres to manage the mental stress. The purpose of this study was to generate new insights into how the patient constructs a new sense of reality when confronted with the malignant brain tumour diagnosis. Within grounded theory methodology, 30 patients with malignant gliomas were interviewed twice, in direct connection with diagnosis, surgery and radiotherapy. In addition, their partners were interviewed, and quantitative instruments (SMMSE, RDCQ) were used as additional references for assessing the patients cognitively and emotionally. Eleven patients were excluded from the final analysis because of cognitive impairment of personality change. Most of the patients were aware of the fact that the brain tumour exposed them to grave danger, but they were also able to use various cognitive manoeuvres to create protection and hope. This process originated from different sources: the body; helpful relations; cognitive schemata; and the handling of information. The importance of the body to raise hope is emphasized. In the discussion we consider this process as an expression of how the patient brings together reality and hope, thus creating her/his own illusion. These findings are also related to adjacent psychoanalytic theory, proposing a theoretical reference with clinical implications when discussing "What to tell cancer patients."