We evaluate the capabilities of Schwarzschild's orbit-superposition method by applying it to galaxies from the large scale, high resolution Illustris simulation. This allows us to assess the reliability of the method in estimating the internal mass distribution of galaxies. The results show that the method is capable of accurately reproducing the observed properties of the galaxies, including their rotation curves and velocity dispersions. However, the method also reveals some limitations, such as the difficulty in accurately modelling the triaxial structure of the galaxies. Overall, our study provides valuable insights into the strengths and weaknesses of Schwarzschild's orbit-superposition method and its potential applications in the field of galaxy evolution.