The "direct" binding free energy calculation method was originally developed by De Jong et al. and later applied to 10 microsecond trajectories by Pan et al. in 2017. We would like to point out that the method is justified on the basis that a sufficiently long single trajectory can be averaged to produce a meaningful macroscopic free energy. However, we will demonstrate that this assumption is not valid, and hence free energies computed through this method using a single trajectory are not reliable. To calculate the binding free energy, we use the following equations which were derived via statistical mechanics by De Jong et al. 75