Two scopes can run at the same time. For example, at the end of the year, a bank executes two activities for each account: add interest and charge credit card costs. These activities can be executed in any order. However, since they both update the account, they cannot execute at the same time.
To ensure that variables referred to within each scope do not conflict, you can enable the isolated property. This property enables serialized access to variables, so that one scope has access to the shared variables and must finish using them before the concurrently running scope can use them.