All it takes is a moment's lapse in attention despite the best efforts of a crew and calamity can occur.
Agreed, and in a high workload scenario or in difficult conditions that lapse can have dire consequences but pilots do human factors training and should be armed against such lapses in benign scenarios such as this.
Apparently, more car accidents happen within 5 minutes of the persons home than anywhere else - perhaps an indication that how ever vigilant we are on the drive back from work, we tend to relax when we think it is nearly done - perhaps a parallel to draw with landing and taxying in - don't switch off until the rotors have stopped.