When started for the first time, the Simultaneous List rule runs all of its child rules simultaneously. How the Simultaneous List rule completes itself depends on the settings entered in it's configuration dialogue.
The default option is for the rule to complete itself after all child rules have reached a complete state. There is also an option to complete the Simultaneous List when the child rules have reached a “was complete” state, meaning that all the child rules have reached a complete state at least once.
Alternatively the Simultaneous List rule can be configured to complete itself once one of the child rules has completed. In this case all other child rules are abandoned.