Quick Connect synchronizes in a 1:1 relationship. In order to maintain this 1:1 relationship, a mapping is required to be created between a source system and a target system. The mapping criteria is used to determine which single object on one side matches a single object on the other side. With that being said, it's important to choose criteria that is going to be unique, such as the samAccountName attribute in Active Directory, since no two accounts will have the same samAccountName. Choosing a property such as EmployeeID can sometimes cause issues if a user is rehired and a second HR account is created with the same existing employee ID.
If the source system has a single 'John Smith' account and the target system has 2 'John Smith' accounts, the mapping is what allows Quick Connect to determine which of the 2 accounts on the target belongs to the single account on the source. In this case, a mapping of SAMACCOUNTNAME > SAMACCOUNTNAME would suffice and would map as follows:
|John Smith (jsmith)||⇐⇐⇐ MAPPING ⇒⇒⇒||John Smith (jsmith)|
|John Smith (jsmith2)|
For information on how to create a mapping, please refer to the Administration Guide: