Whenever someone, A, sends a confirmation, apparently A thinks there may be a risk that the other person, B, will not come unless a confirmation is received.  

But it is possible that the confirmation from A is lost along the way. That means that if A doesn't hear anything back, there is indeed a risk that the confirmation was lost and B will not come. 

Perhaps this is enough reason for A not to come.  Hence, B, when receiving a confirmation, may worry that A will not come, unless B sends another confirmation.  And so it continues.