It depends on what position you are aiming for. If you are aiming for a LSS trainer role, it would be important to have a reasonable grasp of the underlying statistical principles, if not the the actual formula. For other roles, where you may have to lead a LSS project, in whatever else may be your area of competency, you can either rely on the statistical software and take the help of an LSS BB or MBB, where you need help. One of the main reasons why these applied subjects did not (and maybe still do not) get enough of buy-in was that many used to get put-off on the stat part. In the earlier days one had to use tables and calculators to do the workings, but now, thanks to the advanced software packages available, we are able to perform that part with ease. So, if we keep harping too much on the theoretical part, we may once again kindle the discouragement. We need to be careful and practical in this approach.