Bad Instructions

There is a widespread misunderstanding of the meaning of CONTACT.   In many riding schools you will often hear the instruction 'MORE LEFT REIN, MORE OUTSIDE REIN'. Pulling on or shortening one rein or the other does nothing to improve the connection or your horses way of going.
The contact (or connection) COMES FROM THE HIND LEG!!!!!

The horse will offer a contact when his hindlimbs become strong enough to raise the back and allow the horse to travel in a balanced way. If he cannot stretch out to the bit, the hindlimbs must be activated to create a stronger push forward. If the reins are shortened so that the rider has a direct connection to the horses mouth but the horse is not stretching over the topline to reach for the bit, he cannot work properly over the back, and thrust is suppressed.

The trainers should instead shout MORE INSIDE LEG to get the horse to bend correct and stretch the outside rein.
Pulling on the reins will disrupt the horses balance and make the job even harder for the as yet weak hindlimbs.