A common thing seen in sport or exercise is people rushing through the motions without care for quality of the movement being done. sport and exercise is very energy demanding and that's ok because when we move with good form, we are moving in a way that is most energy efficient for our body! The problem is when we just want to be done or are emphasizing quantity or quickness, the efficient form falls apart and we become sloppy.
Poor form is energy expensive which will exhaust/fatigue you. If you are tired, the ability for you to summon the strength to keep good form is weakened, which just drives us into even worse form and thus even more fatigue and junk form until you break the cycle through enhancing your capacity or end in injury