People communicate with each other in all sorts of ways, such as verbally, by writing, by sight, by sound, by touch, and by smell. In all of these ways, when two people frequently get together, if they are really paying attention to one another, they use some or most of these various ways to get to know the other person at a level which is far beyond cursory, and is typically classified as intimate. However, as good as people can be in noticing the big things as well as the very vital little things about one another, they are limited to how much that they can really know about someone by virtue of the fact that they are not inside that other person's mind or that other person's thoughts.
That is to say, people from time-to-time will say one thing but inside their mind, they will be thinking the very opposite thing or a contradictory thing. So too, the thoughts that people express in their minds about others or even about themselves can vary from being very positive and beneficial to being very negative and hurtful. Most people keep thoughts that are contradictory or hurtful within their mind and seldom express them to someone that they really care about, except when they lose their temper or are under an immense amount of stress in which, those thoughts are expressed out loud, and often expressed with some real regret.
So too, within most people are thoughts that are very private, so private, that they are reluctant to express those thoughts out loud, although, if these thoughts are a strong component of their true persona, they may leak out in their words so spoken and actions taken. However, a lot of people make it their point, that even with those that they are closest to, that they will not express certain thoughts, or certain stories, or certain things, because they fear that if they do, the person that they care so much about, will change their opinion or their feelings about them, and they do not wish to gamble with losing their respect, or love, or company.
This signifies, that those that live within a construct in which they are forever hiding who and what they really are, in order to project something that is not fully true are often doing so, out of the fear that those that they are closest to, would not love them if they knew who they really were. While it is true, that people should not necessarily be an open book to everyone, for intimate secrets and thoughts, can be and have been used to hurt and to debilitate people; it is also true that those that fear that they will not be accepted by their best and truest friend, if they knew who they really were, are basically saying that they fear that the love and respect so expressed to them, is a qualified love, which is based only upon something that fundamentally is not wholly true.
The best way then to deal with this conundrum, is to test the waters of that love, by disclosing some of those thoughts to your closest confidant, and to thereby adjudge their reaction forthwith; for if such is responded to with judgment and condemnation, then proper discretion of any further disclosure is probably the best course to steer, in recognition that true love, judges not, is unconditional, and wills the good of the other. For it is important to acknowledge as well as to remember that if your best friend cannot see themselves in you, and your weaknesses as their own, then they are hiding their own true identity from you.