This paper aims to understand how the difficulties associated to the insertion of sustainability in engineering education are related. From the literature review, eleven difficulties were compiled and posteriorly, a panel of experts was conducted to divide them in two groups, named "difficulties associated with structure and planning" and "difficulties observed in didactic practice". These groups were used as a base of a questionnaire by survey, with lecturers who work with sustainability in engineering courses. The collected data were analysed through Structural Equation Modeling. A causal relationship between the two groups was verified through the present research, that is, the greater the difficulties associated with the structure and planning, the greater will be the difficulties observed in didactic practice. The results of this paper may be used by researchers in their future studies and by lecturers and coordinators as a guide to the insertion of sustainability in engineering education. The authors believe that these results may contribute to the engineering education improvement.