It all depends on how it's written. If it's written suddenly in the opposite of what's been previously established, even fictional readers can find it hard to believe.
Comics pose this huge problem because they switch writers so frequently. It's often times difficult to get footing on what the current canon even is in them.
Things can easily just not make sense in how they are written. Characters do typically have established personalities and traits. Any transition has to feel organic to still be believed. Especially by those who have long read a certain character or story.