Always judge a book by its cover

Nah two contradictory statements can equally be true. It's sometimes not true you can judge a book by its cover, I've had people tell me how I feel and how I am which is the polar opposite of how I felt. People judge as to how they are sometimes, not how someone else is. If you are a liar, you'll think that everyone else also lies.

However, it's also equally true that it doesn't take a lot to see warning flags of someone and that sometimes you do need to believe what you see literally and to not gaslight yourself when something is amiss.