Difference between affirmations and believing a new thought

What’s the difference between running an affirmation (a sentence/thought in one’s mind) and practicing a new belief daily (running a sentence in one’s mind?
Brooke talks about affirmations as being bogus because it’s a thought that doesn’t resonate with us, so running it in our minds will never work.

But in the homework of “believing new things” that’s exactly what she asks us to do – choose a thought we don’t yet believe (aka: it doesn’t yet resonate), and then practice it every day.

This is what people do with affirmations. Please help me see the difference! Thanks!