The problem below has been coded to achieve the desired result. We are just looking for a definitive answer of why the error occurs.
We have a target table we are inserting into with a target column datatype of varchar(4).
We have a source table with the source column of datatype varchar(7).
In the source table all the records are 4 characters long except for one record which contains the value of "UNKNOWN".
We got the error that string or binary data would be truncated when running the insert. This made sense if one of the records being inserted was the record with the value of "UNKNOWN". That record wasn't explicitly excluded, but it wouldn't have been part of the data set being inserted. Why does the error get thrown?