Character Arcs: 'Want vs. Need' pitfalls for new writers?

Hey everyone,

I’m currently outlining a new feature, a sci-fi drama, and I'm really digging into the 'want vs. need' dynamic for my protagonist's arc. I've tried a few different approaches in the past, including mapping out internal/external journeys rigorously, and sometimes it feels like the arc clicks, other times it just feels... clunky.

Looking back over your own experiences, what are some of the most common mistakes you see new screenwriters make when trying to build character arcs based on 'want vs. need'? Are there specific pitfalls that lead to arcs feeling forced, underdeveloped, or simply not surviving the edit? I’m particularly interested in things that feel right on paper but fall apart in execution.