Brienne of Tarth, in Game of Thrones, is noble in her cause, and intends to uphold an oath she swore to Lady Stark to keep her children safe. But she is also a bit naive about the nature of the world in which she lives.
Brienne thinks she can bring Arya to a safe place, wherever that is. But as The Hound so eloquently reminds her:
“There is no safety you dumb bitch. And if you don’t know that by now, you’re the wrong one to watch over her.”