Dataguard mandatory destination unavailable causes primary to terminate

I'm trying to confirm if our situation is expected or not.

We have a dataguard physical standby setup as the lone destination for redo's and archives and it's running in real time apply. 

The issue I'm having is I can't start the primary if the standby is unavailable, further, if the standby becomes unavailable while the primary is up, the primary will terminate.

My speculation is that is caused because the standby as a mandatory location.   I just can't find any documentation that states the primary will terminate if it can't send logs to the standby.