What are some elements of the prototyping process that are difficult to manage?

The following remark was overheard at a meeting between managers and a systems Analysis team at the Fence-Me-In fencing company: “You told us the prototype would be finished three weeks ago. We’re still waiting for it!”

Comment on the importance of rapid delivery of a portion of a prototyped information system.
List at least three elements of the prototyping process that must be controlled to ensure prompt delivery of the prototype.
What are some elements of the prototyping process that are difficult to manage? List them.
Instructions:

Your essay should be approximately 400 words.
Be sure to use proper APA punctuation, spelling and grammar; points will be deducted accordingly.