I learned a new term today, but if you have a military background you may be familiar with it.
It is "Mission Creep". From Wikipedia, Mission creep is the expansion of a project or mission beyond its original goals. The term often implies a certain disapproval of newly adopted goals by the user of the term. Mission creep is usually considered undesirable due to the dangerous path of each success breeding more ambitious attempts, only stopping when a final, often catastrophic, failure occurs. The term was originally applied exclusively to military operations, but has recently been applied to many different fields.
How appropriate, I thought, when a simple project such as "I'm just going to fill in the blank suddenly becomes a major undertaking rendering your car jackstand bound for an unexpected period of time. The effects of mission creep are seriously exaggerated by 1) underfunding/unrealistic budget projections, 2) procrastination and 3) unsubstantiated optimism.
At least now I know what to call this affliction...