What was the great simcha when they saw the "tcheiles" of Mordechai??
I am guessing because it finally proves that all of the people who wear tcheilis were right all along.
But maybe that is pashat in the pasuk at the end of the Megilla that Mordechai was רצוי לרוב אחיו and the gemara darshens ולא לכל אחיו. Why? Maybe because they didn't hold of his tcheiles...
