Mistakes in screenplays

Unlikable protagonist

You must make the hero feel like "one of us." Could this happen to me? What would I do then?
The viewer must be emotionally engaged. Without that, they'll quickly lose interest.

The invincible hero

Another common mistake is creating an omnipotent hero who's almost unbeatable.
That makes the film boring - the viewer feels no tension because the hero is never in danger.

If the hero is unimaginably strong, create a force at least equal to or stronger than them.
The audience must fear for their favorite character.

You can also introduce a weakness that neutralizes their power - for example, Superman becoming weak near kryptonite.
Without it, the script would go like:
"The enemy attacks, Superman arrives and saves everyone - again and again."
Who would want to watch that? That's a recipe for boredom!