Don’t judge a book by its ______?

The correct answer is: Cover

The absolute example to make a good living. The direct meaning lies in this is, every book has its own content. Some may be the best, some may be the worst. Some will give moral values, some will entertain us. Each and every books' cover will be different which depends on the content. So, by just reading the cover page, we should conclude that this book will be like this, that book will be like that. Unless we read the content, we will not be knowing the value of the book in  the cover page. Likewise, by seeing people's outer appearance, we should not judge them. We should get to know about them and their character. Not everybody are same as they appear or act outwards.There will be some kind heart inside as the best book contains the best content.