It's the usual ever returning confusion again. It's the fuse behind the wire, that protects the wire from heating, burning and starting a fire. To take it practical: If the consumer is a 2 watt bulb, the wire could be extremely thin, calculating and following the previous advice. If the fuse would be large, say 30 A, (maybe because there are other consumers connected to that same fuse too) and that little bulb would short out, the fuse would not blow. Instead that thin wire would get hot, very hot, and create disaster.