Whenever someone (A) sends a confirmation, apparently she thinks there is 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, which means that if A doesn't hear anything else, there is indeed a risk that the confirmation was lost and B will not come; and perhaps this risk is enough reason for A not to come herself.  Hence, B, when receiving a confirmation, may worry that A will not come, unless he (B) sends another confirmation.  And so it continues.