Top 20 reasons (even though I can think of 100)

1.  You haven't thought about the ceremony too much

2.  You don't write down your vows or speech

3.  You try on your shoes the day of the wedding

4.  You pack for the honeymoon last-minute

5.  You assume you'll coordinate anything day-of

6.  You haven't thought about transportation for your guests

7.  You plan to use an iPod for music

8.  You do the seating chart last-minute

9.  You did not register

10.  You have a cash bar

11.  You don't do any hair or makeup trials

12.  You don't have a day-of itinerary

13.  You stress out so much you don't enjoy anything

14.  You don't stick to your budget

15.  You hire a friend or family member as your photographer

16.  You plan your own bridal shower or bachelorette party

17.  You ask someone to be a bridesmaid out of obligation

18.  You decide to do your own hair, makeup or flowers

19.  You don't have a Plan B for an outdoor wedding

20.  You behave like a Bridezilla