Explain the Rationale Behind a System Choice

“Alice came to a fork in the road. 'Which road do I take?' she asked.
'Where do you want to go?' responded the Cheshire Cat.
'I don't know,' Alice answered.
'Then,' said the Cat, 'it doesn't matter.”
- Lewis Carol
Alice in Wonderland 
In other words, if on one hand you don't mind what a system does there is no need to know why it works the way it does. If on the other hand you do mind what a system does and you do mind that it works and that the people using it use it correctly then you better explain early on and often the 'why' behind the choices that are being made in the organization project.
We once worked for a client who did not explain to the end-users the selection of a certain system had more to do with dislike of the previous system and its system provider and less to do with like for the new. This turned out to be a costly mistake as the users really liked the old system and never really accepted the new system. After a few years the organization had to back track on its steps and go through a costly revision of the system.
If this organization would have explained the reason for switching had more to do with a falling apart between them and their provider they would have probably still have had to do a lot of convincing but in the end the system would have been accepted.