Luck is a hidden feature that affects gameplay in subtle, but often noticeable ways. At the start of each day, your luck for that day will be determined randomly. Luck can be manipulated in several ways, such as by wearing a particular type of clothing or arranging furniture in a certain way. Some items can also affect your luck adversely, such as the King Tut's Mask.
Types of luck
Katrina, the Fortune Teller
Katrina is a purpleish cat that sits in a tent where Crazy Red has his tent. She visits your town randomly. For 100 bells, you can have your fortune read. She will pull a card after saying her words, and say something like, "Balloon, in it's natural state." And say words that can line up with good luck or bad. It is completely random. If she gave you bad luck, you will trip and fall, and bad things will happen, concerning fishing and bug catching, but if you got good luck however, villagers will be nicer, and more better things might happen.