While you are waiting at a stop sign to turn right, if a vehicle approaches from the left with its turn signal on, you should wait until the other vehicle really has started to turn. Only then should you start your turn. Drivers may make mistakes or change their minds. The driver of the other vehicle may change his or her mind at the very last moment and decide to go straight through the intersection after all. Or the driver of the other vehicle may have switched on the turn signal by mistake and really intends to go straight through the intersection. If you assume that the other vehicle really will turn as its turn signal indicates, you risk a collision with it. Part of defensive driving is knowing how to cope with bad signals and bad drivers.