The point of such concealment of thoughts take on many layers. It could be lying to someone. It could be evading an inferior impression towards someone. It could be an obligation to handle needed social contexts/politics. Or it could even be because one is writing a thesis. 

But the above mentioned are the simpler versions. Concealment of thoughts go beyond just because one wants to be immoral, vain, safe or that its a needed rule for the proper framing and expression of justifiable ideas/thoughts. 

Theres a concealment that occurs without such precise and identifiable intentions. A concealment - actually, concealments - that are committed by every individual at points in time over issues that are somehow within a momentary phase. In other words, you just don't say some things sometimes cos its either not the right time to or its just not a right thing to say.

So moments like this pass. Many are probably shrugged off, ignored and forgotten, especially if the person whom such a moment of concealment (on both sides) isn't, bluntly speaking, someone who really matters to you a lot. 

But when moments like this happen to those that matter to you - thats when the danger arises. Instead of being shrugged off, these concealments fade into many other areas. For example, the evidences that an Iago would coax an Othello into believing (ie Assumptions, misunderstanding, mistrust and then murder -_-). Another example, a misinterpretation of what A really is, although both can appreciate that A leads to B.  A last example, your grandfather wants you to celebrate his birthday and you know he likes chicken rice. You know he likes and would probably expect things to go in a certain way with regards to a birthday and a relation to that and chicken rice. But when things turn out... it was not supposed to be in that way. 

The thing that this concept reveals, is that we cannot communicate to someone perfectly. Of course, its probably already enough when we can talk to another person, learn more about the person, know the person, understand the person, trust the person etc. I'm not questioning whether the limits of language weakens such a bond. 

Rather, I'm thinking that perhaps the test of such a bond does not lie in how much conveyance is understood on a verbal plane. Instead, it may be found in the silence. 

How and what one feels when he is silent with someone would tell a lot about the bond (and I'm not only referring to how comfortable he/she is with the silence) After all, the concealments that occur can be something mutually understood between both sides - and such a understanding is best concealed and appreciated, in a silence.