What is a 'Non relevant sub topic'?
This sounds serious!!It can be.
You need to keep your sub topics relevant to the Main topic.
It can be about you but...
Example - One of your sub topics could be about Will I get to see space?
BUT NOT..
Sub topic 1 - Sex robots (yes, someone has used this )
Sub topic 2 - Alien wars (nothing stopping an Alien war happening now)
Sub topic 3 - Star Wars (it's science fantasy)