If you’ve been hit by a bad beta reader you’ll know it. Emotionally, at least. You’ll feel panicked, anxious, FULL of self-doubt, and lower than low. However, your rational mind will try to talk you out of it. Writers need to be thick-skinned, it will say. All feedback is valuable in some way, it will add. But your gut will feel otherwise. Deep down, you’ll know that something is off. Something is wrong.
And then, if you don’t find another outside party to confide in who can give you that reinforcement and validation you need to trust your gut, you can quickly spiral out of control and lose all confidence in your book.