Pat Helland's got a fascinating post on his blog called "Accountants Don't Use Erasers." It's a must read, and here are the two major points:

1) You don't really ever delete ANYTHING.  As a matter of fact, you don't update anything either... You just accrete new knowledge and distill new implications based upon your increasing knowledge.

2) People (and applications) will act on their partial knowledge and then, when learning new facts, take new actions.   Sometimes, you realize you shouldn't have taken the action but, gee, it was a great decision based on what you knew at the time.   Since you weren't omniscient, you could have perfect knowledge and could make perfect decisions... Shit happens and you deal with it.

The most important part of which is, of course, the last sentence.

From the data warehousing standpoint from which we are currently working, the "you don't really ever delete ANYTHING" part is doubly true. Nothing in the warehouse should ever be gotten rid of it...only accounted for within your analysis (via exclusion or whatever).

From the psychological point of view, the second point is so obvious, it almost doesn't even need to be stated. It also ties in quite nicely with my previous post on how the business side of a project tends to "anxiously anticipate failure." They are making decisions based on an imperfect understanding of the process. In addition, even if they understand the process, they are a level removed from the intimate understanding that the developers have. Hopefully, armed with this understanding, we can help them not be so cup-half-empty.