Just because an exercise is difficult doesn't make it good. Just because an exercise is difficult doesn't make it appropriate. Just because an exercise is difficult doesn't mean you should be giving it to your patient.
Far too often I've witnessed therapists, particularly new grads, prescribing exercises for which they have no justification, rationale, or explanation more than "it's hard." As physical therapists we are in an extraordinary position that allows us to provide corrective exercises tailored to the needs of the individual. We get to assess the patient, determine specific deficits, and intervene accordingly. Throwing random exercises at a patient not only devalues what we as physical therapists do, it does your patients a huge disservice.
If you've been doing any kind of functional movement reading these days you've inevitably stumbled across some sort of explanation of the importance and interplay of proper form, repetition, and subsequent motor control. One of my favorite phrases has come to be "don't practice until you get it right, practice until you can't get it wrong." Prescribing an exercise based on sheer difficulty generally results in sacrificed quality of motion, poor performance, and to be blunt, a waste of everyone's time.
Gray Cook does an excellent job of laying out a pretty basic system for progressing a patient through exercises in the 4x4 matrix. Now, my goal isn't to create a bunch of SFMA/FMS converts, but rather to show you that the age old phrase "you gotta walk before you run" applies to more than just Hallmark moments involving a dad talking to his son while sitting on their stoop dispensing invaluable life lessons. Having your patient do single leg deadlifts before they've even come close to mastering proper quad rocking doesn't just set them up for injury, it reinforces inefficient movement patterns, incorrect techniques, and inappropriate strategies. Long story short, it makes your patient really good at being really bad.
While it may be tempting to be known as the therapist with the most difficult exercises in the clinic, consider the benefits to be had by all if you operated under the moniker 'the PT with the the most efficient and effective exercises.' Admittedly, not the sexiest, but achieving a 50% reduction in symptoms in just one or two sessions is pretty impressive. Clever nicknames be damned.
So whether you're a new grad or an old dog, don't be that guy. You know, the guy with 50 exercises on the therex list and the need to use every piece of equipment in the gym in some crazy way. Just because it's difficult doesn't mean it's good, and in order to be good, it doesn't have to be difficult. Allow your patients to walk before they run, and remember, just because they're sweating doesn't mean you're doing a good job.