In my view,one cannot wholly understand the other no matter how much of friends they are.
Even relatives can't in any way arrive at this about each other.
Not even someone with whom you have shared a bed for years.One of the abilities that the creator withheld from from us (humans) during the process of creation is knowing what the other person really has in mind or at heart and surely this continues to be the main influence of inevitable mystery about each other.
You can be at table with someone that is planning to have you totally brought down and destroyed while laughing and doing high fives,generally 'enjoying'. It's possible and I believe this has happened in many instances before.
You be madly mad at someone who wishes you all the best in your endeavors.This too is very possible and I believe it also has happened before.

We continually try to impress people that really have shown us that our advances are unappreciated persistently with hope of a change in mind.
In very normal situations,a blood brother/sister can deny any form of relation to you in situations where he he/she is in pursuit of person gain.
And yet again...