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Type 1 diabetes (T1D) remains associated with suboptimal glycemic control in a substantial proportion of individuals despite major advances in insulin formulations and technological systems. This apparent paradox highlights that glucose control in T1D is not determined by technology alone, but rather emerges from the interaction of multiple biological, therapeutic, behavioral, and psychosocial factors. In this structured narrative review, we examine the main determinants that continue to limit optimal control in real-world practice. Pathophysiological barriers include residual or absolute insulin deficiency, impaired counterregulatory responses, chronic or acute insulin resistance, hormonal changes related to puberty, the menstrual cycle and pregnancy, physical activity, and advanced renal disease. Therapeutic and technological progress has improved glycemic safety and time in range, yet insulin therapy remains an imperfect substitute for physiological insulin secretion, and the effectiveness of CGM, insulin pumps, connected pens, and AID systems remains highly dependent on sustained and appropriate use. Behavioral determinants such as treatment adherence, meal bolusing, carbohydrate estimation, physical activity management, and technology misuse continue to be major drivers of glycemic variability. In parallel, psychosocial factors, including eating disorders, anxiety, depression, stress, socioeconomic vulnerability, and shift work, strongly influence self-management and may further aggravate metabolic instability. These determinants interact dynamically and bidirectionally, creating self-reinforcing cycles that help explain why recommended glycemic targets remain difficult to achieve. Improving outcomes in T1D therefore requires moving beyond a technology-centered model toward an integrated, patient-centered approach that combines technological innovation with therapeutic education, psychosocial screening, and individualized care across the life course.