An observation coupled with my personal experience is that people starting something physical without a proper screening, like krav maga, tend to run into some issues later down the line. This is, again referencing from my personal experience, is also often mirrored in “fitness” classes.
Without addressing any weaknesses, faulty movement patterns (biomechanics) and unconditioned joints they throw themselves into their new found passion. Only to find that as they advance that things start getting harder, not easier. Even when the techniques don't get more advanced, the demands are more advanced. Things start becoming more neurologically and physically demanding. Then the machine starts breaking down. One injury, but soon you return after the supposed rehab period. Another injury follows. Now you need a longer period off, then the long break leads to stopping all together. Any sports has trainers and their models that do have a better approach in teaching and training that supports enhancing biomechanics., whereas other “schools” might not have that. There are a lot of parameters to keep in mind. Like the trainer, their coaching model experience and education.
What I feel strongly about is the person takes a smarter approach before they go into anything physically demanding after being inactive for what possibly has been decades. Focusing on fixing their biomechanics (movement patterns), conditioning and prepping joints, strengthening tissues in “improper” alignment. The general temperament towards that seems to be negative as most people think it's demotivating. But this beginning is the inertia that sets that ball rolling. The myth of Sisyphus speaks of Sisyphus his punishment of pushing a boulder uphill for eternity, each time he gets to the top the ball rolls back down and he starts all over again. Imagine there is no hill now and that my title is a poor choice of analogy. If we begin at the start, you'll have to push hard to overcome that initial inertia until the ball even moves. But once it's in motion, the inertia (resistance) is bridged and you're doing well. The reverse is true when you neglect to improve your tissues, mechanics, joints and everything else. You bridge the inertia rapidly but the ball starts getting heavier to push, the resistance adds as you go, instead of decreasing.
If you do all the work you should do in the beginning: that's work you never have to do again, provided you don't have a major injury (which the prep and optimizing mechanics aims to mitigates/ prevents). If you don't it will catch up with you in the long run, which is even more demotivating after you got so “far”.