Most have heard some version of the adage, "You can never tell a book by its cover." The phrase first appeared in print in the 1946 novel, "Murder in the Glass Room, by Edwin Rolfe and Lester Fuller. Even then it was an adaption of "You can't judge a book by its binding", from the Journal of American Speech (1944). Some purport that the phrase can be traced to Roman author Juvenal who wrote in Satires, "Fronti nulla fides," which translates as, "Never have faith in the front." as far back as the 1st or 2nd century AD.
Like many adages, this is not uniquely true. You can read the entire book and as you close the cover, you will note that the words on the cover describing what's inside has not changed. And, no matter how many times you read the book, nothing about the book changes. Neither the cover nor the content change with multiple readings. The cover looks the same and the description remains the same. The words inside say the same thing.
What does change is our understanding of the book. As with our relationships with others, every time we open the book and study it, we learn a bit more about the author's original intent. Or, in some instances, we mistakenly come to believe the opposite of what the author intended, depending on just how vivid our imagination is and how much we want to believe our own version of truth rather than accepting what is real and intended.
The words in books can form ideas in some readers that spread like a virus, infecting and destroying the truth of the matter. The same thing may happen with relationships as we allow our imagination to wander in search of our own truth. That truth will depend on how we perceive what it is that we want or need at the moment.
Those who attempt to judge you with either a single or multiple reading, for the most part, rely on the adage that the outside and inside are somehow different and that the outside is not to be trusted. That they somehow need to construe what they will about character. For those who believe that you cannot judge a book by its cover, they will never know who others really are - only their own ideas - which can never be correct.