What key collaboration aspect does C40 emphasize among its member cities?

C40 emphasizes the sharing of best practices as a key collaboration aspect among its member cities because it allows for learning from one another's experiences, successes, and challenges in addressing urban climate issues. By openly exchanging strategies and solutions, cities can implement proven approaches more effectively, leading to quicker improvements in sustainability and resilience. The focus on sharing best practices fosters a supportive network where cities can collaborate on climate initiatives, thus enhancing their collective impact. This collaborative mindset is essential, as urban areas around the world face similar challenges but may tackle them through different methods that can be adapted and refined based on shared knowledge.