Weiland is of the mode that how a character changes over a story is the plot.

She generally separates out the internal state of the protagonist from their external state.

She has 3 arc types: positive, flat, and negative.

Positive arcs are the typical Hero's journey (along with the other 5 archetypes of the title). The protagonist comes back changed in a good way and the story world is better in gestalt. Her concepts of the Truth, the Lie, the Ghost, the Need, and the Want are all intertwined here and are developed in other books and on her website. Positive change arc are 'comedies' in the classical Greek sense.

Flat arcs have the protagonist already in possession of the Truth and mostly have them affecting the story world with that Truth. Sounds boring, but they tend to be the most memorable characters for audiences.

Negative arcs come in 3 varieties that I won't bore you with. Generally, the protagonist rejects the Truth and embraces the Lie. These are 'tragedies' in the classical Greek sense.

Her overall structure is on a 11 beat framework that fits nicely with 3, 4, or 5 act structure (she has a lot to say about that).

I would highly recommend her work for deep dives into narrative and story structure.

John Yorke's Into the Woods is also a great read:

https://www.amazon.com/Into-Woods-Five-Act-Journey-Story/dp/...

He dives more into the 'why' when it comes to the reason we tell stories at all.

Both he and Weiland (among others) have convinced me that 'story' is one of the more powerful things in our world.