Smart cities are being advocated to solve the excessive urbanization. They are supposed to be more efficient, more connected and more sustainable. However, long-term sustainability cannot be achieved in a real situation unless we seal the loopholes that still prevail in our current efforts. The main issues are: integrating renewable-energy solutions to reduce carbon; applying the principles of the circular economy to consume fewer resources and produce less waste; and ensuring that every resident of urban areas is able to access available urban resources and services that are usually not evenly distributed. In this article, the sustainability challenges are gathered together and demonstrate how they can be addressed by use of technology, provided that the technology is supported by good governance and accepted standards. A city that strategically connects its smart-city strategies to the United Nations Sustainable Development Goals, as well as to the appropriate national, industry, and IEEE standards, has left its technology-centered viewpoint, where people, the environment, and long-term resilience are prioritized. Ultimately, to head in the right direction and create the sustainable urban futures, we need to combine the latest technology with equitable policies and plans that would respond to climate change. This is when smart cities will bring a sustainable advantage to the lives of people and the planet.