The final word on CRM looks like this:
Your CRM requirements are the real world problem situation, on the left. Despite our desire to simplify our problems, the true nature of your CRM requirements is murky and somewhat open to interpretation.
The CRM systems available to you are the square models of purposeful activity, on the right. The task is to select or customise the most appropriate system based on your understanding of your requirements.
You compare the situation before and after implementation, also considering social and political analysis. A CRM system is an information system, meaning it involves people. Are the people who are supposed to be working in the system using it as intended? Or are they working around it, complaining about it behind your back?
The bigger your company the more real this problem becomes.
Eventually we are left with a new real world problem situation, and the cycle begins again. With cloud-based systems the cycle can begin again fairly quickly, as it is easier to add or remove system functionality.