The concept of the Smart City is the answer for the majority of the challenges of an increased rate of urbanization. However, the implementation of the ideas of the Smart City faces some difficulties. It is a necessity to correspond to the sustainability pillars and the decisive role of the population in all processes, and correspondently the necessity to comprehend what factors influence the decision-making process. The research goal of this paper is to analyze the factors determining the decision of the population of multi- and one-family houses to sort waste. The data were collected via population survey of the Vidusdaugavas region of Latvia and semi-structured interviews of municipal councils’ representatives. Both parties—population and authorities—have mentioned the existence of more negative factors of waste sorting in their life than positive ones. For authorities, the most important externalities of waste sorting have an economic nature, while, for citizens, the factors of convenience are not less important than costs. The problem was considered from the position of municipal authorities and the local population, and the identification of problems and misunderstanding is a possibility to start effective communication between the two parties. Moreover, the analysis of the literature has shown that Scandinavian countries and west European countries, which started their way towards implementing smart sustainable cities significantly earlier than Latvia, had the same stages. The most important factor for constructing a smart sustainable city is the changing the way of thinking of population.