We synthesize findings from stakeholder consultations conducted across seven case studies (France, Hungary, Italy, Kenya, Nigeria, Pakistan, and at the EU level) to identify implementation barriers for energy transitions that extend beyond technical feasibility. Through workshops and interviews engaging over 100 stakeholders from government, industry, civil society, and research institutions, we document challenges that are often underrepresented or operationalized only partially in quantitative energy scenarios. Despite the diverse geographical, institutional, and developmental contexts represented, stakeholders demonstrated substantial convergence on eight core barrier categories: social acceptance and behavior, economic and financial costs, governance and policy coherence, political power and vested interests, regulatory and administrative barriers, technology and infrastructure constraints, workforce and skills gaps, and industrial and supply chain bottlenecks. These barriers often operate as interconnected challenges—for instance, high upfront costs for clean technologies may undermine social acceptance among lower-income populations. The findings suggest that practitioners possess a sophisticated understanding of systemic implementation dynamics that formal models currently often underrepresent, and highlight the need to integrate social, political, and institutional factors into energy transition scenarios. Without accounting for these constraints, technically coherent transition pathways may prove difficult to implement, potentially misleading policymakers and eroding public confidence in the feasibility of sustainable energy futures.