Katrina the fortuneteller in Animal Crossing: New Leaf often gives me a prediction of good or bad events, then tells me an item is the key to it.
Generally speaking, how do I decipher her prophecies?
In New Leaf, Katrina inlcudes a wearable item in her fortunes. If you wear this item, it will increase your luck until 11 PM on that day.
Taken from Thonky's guide:
"In Animal Crossing: New Leaf, your luck is random every day. Different good or bad things can happen to you based on your current luck. There are 5 types of luck: money luck, friendship luck, love luck, item luck, physical luck. Each of these can be good or bad each day."
There's a lovely little chart about luck there as well.
So let's say she said there is a loss of money, it means you have to wear the items she tells you to wear, or you will somehow lose money.