Editing mistakes are inevitable 
Everybody, without the need of any prior knowledge or practice, can start editing the Waze map. Therefore, Waze accepts the risk that users make edits that seems logical to them, but lead to undesired results. The Waze community is enthousiastic and active, so the mistake will often quickly be noticed. A more experienced editor will contact you to correct the mistake or do the correction himself. It is not meant as criticism, but an encouragement to learn more about editing.