Anyone who has been involved in an IT projects like developing an online store will also have been involved in project issues and problems so this article "On the 15 ways to screw up an IT project" in CIO would be a timely reminder for you but also great as a learning opportunity. The most common issue that I have found in IT projects that derails the process is scope creep. It can happen to projects big and small. Scope creep is generally blamed on poor project management. However sometimes the project manager and technical people delivering the project will have no control. Even signed statements of work and agreements will not necessarily stop scope creep.
Scope creep is about end use expectation. It is sometimes very easy for a developer to understand and develop functionality for a requirements that is perfectly correct but not as the user envisaged. Users, unfortunately, have a way of changing their minds or opinions even after the work is completed.
To stop scope creep requires either very detailed requirements elaboration with users involved or a very strong will and support position from management who own the project.
Scope creep has the possibility to destroy relationships and cause project, that are otherwise very sound, to fail.
Scope creep is not just the technical development teams problem and needs to be discussed with the project owner and users as early as possible to enable a method of addressing any perceived scope creep.
So like the old adage goes it can be like heading cats and if you have not seen that video then it might lighten your day.