This paper is organized as follows: after having set the boundaries of our discussion and briefly reviewed the computational tools out our disposal as well as the above mentioned usual suspects (Sec. II), we focus on seven different aspects that are detrimental to the calculation of J by means of enhanced sampling atomistic simulations (Sec. III). Finally, in Sec. IV, we assess the challenges ahead and put forward several possibilities we hope the community will decide to explore in the near future.