Mental health is a critical yet overlooked enabler of sustainable development. Its decline impedes progress across the Sustainable Development Goals (SDGs), leading to deteriorating educational outcomes (eg, falling OECD PISA scores), reduced economic productivity, higher health costs, and exacerbated inequalities in both developed and developing countries. Delays in achieving the SDGs, together with increasing climate change impacts and biodiversity loss, have led to deterioration in mental health. Furthermore, rapid urbanisation and environmental degradation in G20 countries are eroding traditional, natural, and socially connected lifestyles, heightening psychological distress such as climate anxiety, ecological grief, and depression. Addressing mental health concerns is thus pivotal to achieving the G20’s mandate of solidarity, equality, and systemic transformation.

This policy brief draws on neuroscience and psychology to highlight the critical role of emotions, like happiness and sadness, in human learning and decision-making, particularly in the face of an uncertain future. It demonstrates how emotionally shaped memories of past decisions can perpetuate behaviour and choices that may no longer be relevant or effective in addressing current challenges. Continued reliance on conditioned choices may increase the likelihood of repeating outdated decisions, impeding progress toward a different future, such as achieving the SDGs. To overcome this inertia, the brief advocates for a human-centred approach incorporating behavioural and mental health strategies to address the emotional biases embedded in decision-making processes. In addition, it calls for integrating Indigenous knowledge systems to provide alternative development pathways that inherently include solidarity, equality, and sustainability. It also proposes to incorporate mental health into SDG financing, in line with the Deccan Principles, to support vulnerable groups. Overcoming past patterns of decision-making and behaviour driven by individualism and inequality requires a fundamental shift in thought processes and emotional responses. This shift is necessary to break free from historical barriers and foster sustainable, equitable development and solidarity at a global scale.