In recent decades, the unbalanced development of Iranian cities and the advent of many problems in various social, cultural, economic, physical and environmental dimensions have resulted inevitably in the need to use urban development plans to advance the spatio-physical condition of cities. In this regard, about five decades have passed since the start of the preparation of urban development plans in Iran; but despite gaining a lot of experience by producers and executors of urban affairs, in practice, urban projects have not been able to take a positive step in the direction of programmed development. Therefore, by detecting the causes of unachievability and failure of these plans, it is possible to prepare realistic and executive plans. Hence, this study seeks to investigate the shortcomings of the master plan approved in 2016 in Tabriz and identify the factors affecting its unrealizability by using the qualitative methods (Delphi and case study methods). Among the most significant reasons for the impracticability of this plan, the following should be mentioned: (1) the inadequacy of the design model (positivism, belief system, obligation, inductive reasoning, centrism and being government-centered); (2) inadequacy in the content of the plan (being governmental and non-participatory, inadequate subjectology and collection of irrelevant data, lack of segregation of interventions in different contexts, lack of an organized monitoring system, mere physical emphases, lack of definition of executive financial possibilities, perfectionism, lack of attention to relativism and inflexibility and lack of connection between the elements and components of the plan); and (3) inadequacy of the plan proposals and strategies (emphasis on quantity, incomplete inference, inefficiency and not including all levels and strata).