This usually overloads one area or one component; the end result is a poor training response. I always say hunt with a rifle, not a shotgun.
Training to failure
This leads to failure. Each workout becomes an end unto itself and the athlete starts holding back anticipating the failure thus dulling the ultimate adaptive response.
Over reliance on one exercise or training method
This creates a one trick pony. Highly adapted instead of fully adaptable. You are what you train to be.
Reliance on a machine in training or a modality in rehab
You adapt to that environment, it is an artificial “safe” environment but not the environment you need to perform in. Sport performance occurs in an information rich dynamic environment.
There are none! I have learned that a quick fix is an easy come, easy go proposition.
Crash programs eventually crash, probably sooner rather than later you can’t hurry the process. Adaptation takes time and the time frames for the various components are quite predictable.