An 89-year-old man with multiple medical comorbidities who has been bedbound for a prolonged period is diagnosed with a large transverse colon mass that invades the pancreas. Although not obstructed, his stools are melanotic and he is anemic. The tumor is resectable but would require a distal pancreatectomy and splenectomy. It is unlikely that he would survive this extensive operation. What ethical principle helps to guide decision making in this patient?