Following what Charlie said, if you plan on setting it up that way, I would suggest changing the is empty to is not empty
The way it's set up in the screenshot, only leads that exist will be synced and assigned to you.
It should read:
If: SFDC Created Date is not empty
Assign to: Do Nothing
Default Choice:
Assign to: User: Diana Silva
Like Charlie said, you should be able to delete the text in choice one, click outside of the box and it will say "Do Nothing"