The Rationale for the Rationale:
The Rationale is the reason, or explanation for a requirement. The rationale is very useful to add with requirements because it helps the reader to understand the proper need of that requirement. Rationale gives the proper guidance on the importance of the requirement to the developer and to the tester. Rationale is also known as helpful for the future related activities as well as it separates the different requirements. To find the proper criteria there is a need to be start by finding the description, and rationale which made for requirements.
Deriving Fit Criteria:
Fit criteria is very important for the requirements. It tells about the requirements that are subjective and ambiguous. Some fit criterion need adjusting at some of the points as they are unattainable due to financial or other constraints. It have some measurements for different kind of requirements.
By: Kirandeep Kaur Gill
Source:
Robertson, S., & Robertson, J. (2014). Mastering the Requirements Process (3rd ed.). Upper Saddle River, N.J: Addison-Wesley.
Group 1 Tim Horton's 
Rationale helps us to know about the reason for our requirement as it is important to known why we need that requirement as it helps to also know about the worth of our requirement. In Tim Horton’s the business requirements has its rationale which helps the business analysist get the required knowledge about the requirement representation for all the needed work as the important process of the work.
By: Sachin Chopra
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Fit Criteria are vital to fully explain and understand business requirements. This removes any doubt, ambiguity, confusion, or vagueness that may occur in a requirement. For Tim Hortons fit criteria can really remove ambiguity which is especially essential given the size of Tim Hortons. Any vague assumptions or interpretations could lead to a failed metric or assessment of a business requirement.
-Mark Stabile
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The rationale is not only a guide to help you find the fit criterion, but also a means to help you know when you have several different requirements masquerading as one. The rationale provides the basis for making decisions about how to implement the requirement.
-Haoyan Yin
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