In this context, the challenge lies not in conceptualization but in formalization. Phenomenological treatments of Major Depressive Disorder (MDD), such as those addressing sudden gains, hysteresis, and multistability, strongly suggest that a complex system perspective is highly applicable to this field. However, progress has been hindered by the absence of adequate measurement strategies and foundational principles. For example, there is limited information on defining state variables that can support the formalization of a mathematical model of depression at both the symptom and neural levels. The timescales under which MDD can manifest remain unclear, and there is a lack of theoretical understanding of how interventions at microscopic (e.g., pharmacology) or macroscopic scales (e.g., behavioral therapies) influence the multiscale dynamics of MDD. Despite considerable research and funding in neuropsychiatry, neuroscience, and psychology, significant gaps persist. The cumulative effect of therapies is effective for less than 40% of patients, and the relapse rate among those in remission exceeds 70%. The field still lacks precise diagnostic biomarkers and definitive diagnoses, resulting in advancements in preventative measures and treatments that are incremental rather than revolutionary.