If you have ever learned to drive a car, type on the computer, shoot a firearm or play a musical instrument you have already intuitively grasped the fundamental concept that makes CrossFit so effective: Threshold Training.
Once I am able to get you to perform a movement with sound mechanics and you are able to perform multiple reps consistently without major corrections from me it is now time to start tweaking the intensity, now and only now is it alright to start incrementally increasing load, volume, and/or speed.
Two people send the same email, one knocks it out in thirty seconds but has hundreds of typos and missed letters, the email is nearly unreadable. The other person sends a perfectly constructed email, no errors, no grammatical issues, but it takes them four hours to write. Which person would you hire to be your personal assistant? Neither, we need both speed and accuracy and the only way to develop it is through incrementally establishing good technique and then stressing it to the point of failure, correct the issues, rinse-wash-repeat.
I am going to coach you to excellent technique, then I am going to ask you to go faster, as you speed up your technique will falter, I am going to coach you to better technique without slowing you down, once you are there I am going to speed you up again, when you do your technique will again begin to falter, I will then coach you to better technique… (see the pattern here?) The mistaken idea that we can improve a skill without ever wavering from perfect technique is strangely unique to the fitness realm. We get that a surgeon needs to be good but also needs to be fast enough to finish the surgery before the patient dies, we get that to be able to drive on the highway we need to BOTH not crash into things AND go fast enough to not get honked at or run off the road, the skills you are coached through in CrossFit are no different.