I can't really say it better than this blogger did:
Here’s a list of good surprises: Candy. Flowers. Finding money on the ground. Realizing you finally have enough points on your credit card to get a free flight to Miami. When a friend you didn’t know was in town shows up to your birthday party.
Here’s a list of bad surprises: H.I.V. Herpes. A fetus. The possibility you’ve just been sexually assaulted. Do you see where I’m going with this?