This may be in reference to writing and writers in general, but I think Mr. Hemingway was getting at something a little deeper.

Your characters may do bad thing, they may make mistakes, they may falter. But it is not your place as the writer to pass judgement on these acts.  That task is for the reader.

Your role is to understand and explain to the reader the why they do these things.  Really get into the psyche of your characters.  Give them a reason for why they act the way they do. It will give your characters layers, round them out and draw the reader into our story.  

And yes, this includes your protagonist and antagonist.

Do you judge your characters?