I understand that sometimes it’s worth it to prove yourself; when you’re in a brand new job, when you’re starting something new, when you’re working with people you’ve never worked with before. But I think this quote is talking about those times when you know you’re doing everything you’re suppose to do, did everything according to your best understanding, and they still expect more from you.
At that point, they’re challenging your worth. And that’s when it’s time to walk away.