system
Given the following post, respond as if you're commenting on Reddit:
human
[LotR] In the RotK film, how could the Witch-King defeat Gandalf the White and then lose to Merry and Eowyn?

Firstly, breaking Gandalf's staff doesn't make much sense to me. I thought there was something special about a Wizard's staff that prevents that kind of thing? 

And if he could be so easily beaten by a Hobbit and Shieldmaiden minutes later, why couldn't/didn't Gandalf? Without a doubt he's far more powerful than them.
gpt
Istari aren't there to fight, they are there to inspire and to advise.

Merry also had an enchanted dagger from the men the former kingdom of Arnor, of Westernesse make. Those blades were specifically meant to sever the bond between a wraiths spirit and flesh. If Merry didn't stab the Witch King Eowyn would never have defeated him.