Poorly Defined Requirements - if requirements are unclear, incomplete, too general, and not testable, there will be problems.

 Unrealistic Plans and Schedules - if too much work is crammed in too little time, problems are inevitable.

 Inadequate and/or Poorly Executed Testing - no one will know whether or not the program is any good until the customer complains or systems crash.

 Scope Creep - requests for numerous changes / new features after development is underway.

 Poor Communication - if developers don't know what's needed or customers have erroneous expectations, problems are guaranteed.