A traveler once visited a city where everyone wore blue. Puzzled, he went to a dyer   and said, " Please dye  the handkerchief red."  "I don't know how to dye red." "Then dye it green." "I can't dye it green. There are forty master dyers in this city, and every one of us can dye only blue." "I can dye all color1s," said the traveler, "Hire me and I'll teach you my art." "We never allow a stranger to enter our craft  ", said the dyer. The traveler made the same offer to the other master dyers, but none would hire him. So he began his own dye shop. Folks soon crowded around asking, "What are all these beautiful color1s called?" He answered, "This is red and that is yellow," and so on. Everyone began bringing him cloth to dye. When the master dyers saw this, they quickly apologized for their past insults  , begging him to hire them and teach them his art. This story could be taken as a warning against   _  .
wearing only blue clothes refusing to learn new ways hiring a stranger visiting strange cities