I remember my first commercial project a simple CMS (Content Management System) which helps accountants to communicate with their customers more easily. Main objective was to create simple inner platform in which registered users could upload their checks, indents, drafts, expenses and other stuff. In addition, accountant which registers his users can view the documents, change their category, status or he can create other necessary forms and documents for the client.
It seemed to be very simple especially when the design was ready for use - I just needed to copy the styles file to another location. However, I made really big mistake by going straight to the job. I did not make any plans what I should make first, what I should do second and so on. The only notes were about database tables and their fields.