For example, suppose client #1 lacks the mobility to deadlift from the floor without losing her neutral spine and going into severe spinal flexion when she attempts to hinge down to the barbell. No problem, have her do deadlifts off blocks instead. Suppose client #2 lacks the core stability that is needed to maintain the proper body alignment that is required to perform push-ups from the ground. Rather than have him do totally butchered push-ups from the floor, elevate his hands on a bench and have him do the hands elevated variation until he develops the stability, and technical proficiency he needs to perform push-ups from the ground. For the record, I intentionally used a male for this example as having to modify push-ups (and no, they are NOT called ''girl push-ups), is not just something that is exclusive to females. Many males should be doing this as well.
Over the years, I can't even begin to tell you how many times my jaw has dropped to the floor when I've watched fitness professionals (in person, and often on social media) putting their clients health and performance-oriented goals at risk by making them do exercises that were completely unsuitable for the specific individual. The best coaches are able to modify on the fly, and aren't rigid in their strategies and ways of thinking. Fit the exercise to the individual. Do not try to force-fit the individual to the exercise. The end result will not be pretty.