Before leveraging the output of the simulation to better understand the different types of galaxies that form, and the evolutionary paths they take towards their present day state, we need to ensure that the simulation is a faithful representation of reality. Due to the complexity of the problem, numerical calculations can never fully capture the answer across all scales of space and time. A finite resolution (the size of the smallest details which we can include) means that some processes, such as the birth of individual stars, cannot be directly captured in a cosmological simulation. As a result, we implement many physical approximations, and the burden then arises to ensure that the particular problems of galaxy formation we wish to study are well represented under these approximations. Therefore, we introduce some of the first insights from the Illustris simulation, by first describing this essential comparison against observations: