Bacteria are the main cause of endodontic infection and endodontic failure. If we can remove the bacteria and prevent its re-entry into the canal space, then we can expect success. Separation of an endodontic instrument does not cause root canal failure, rather the incomplete removal of bacterial causes endodontic failure. The follow case demonstrates this very clearly. File separation occurred with initial endodontic treatment. The separated file prevented complete cleaning and shaping of the canal. Upon retreatment, the separated file was not removed, but rather pushed apically. However, the canal was cleaned, shaped and filled to the apex with the separated instrument left in the tooth. The periapical lesion healed and the tooth is asymptomatic and functional. I often explain to patients that a separated instrument is not a big problem, unless it prevents us from completely cleaning and shaping the canal.