I disagree with this statement, because we do not have to tell everything. Friends are not part of my family. Moreover, true friendships does not break by keeping secrets.
Firstly, we do not have to tell secrets to our friends, if we do not want to. For example, in my experience, several friends wanted to know my phone password, but I did not tell them. Sometimes, I cannot trust people, even though they are best friends. Since I locked my phone for my privacy, I do not want that other people use my phone without permission. I could get into trouble, if my friend creates any problems with my phone. However, I will not be able to blame her, because I am responsible for my own phone. Sometimes, keeping secret from other creates less trouble.
Secondly, friends are not my family members. For instance, some people may have a place at their house to store their huge amount of money. However, I think that children will not tell to their friends, because they know that they will get in trouble, if other people steal their money. I consider that most families have their own secret that only they know. Even though best friends are reliable, we must not tell all of our secrets to them, because we do not know everything about them.
Thirdly, real friendships do not break, by hiding anything that is extremely important. We can control ourselves, but they cannot. We can also make a better choice to either tell the information or not. True friends will understand, even though we cannot tell them. Sometimes, my friends beg me to tell her, but I do not, because I made a right choice. Afterwards she did not care anymore, because she did not want force me to tell her, if I do not want to. I think this is a form of true friendship.
In conclusion, we can hide anything from our friends, if we want to, it will not cause our friendships to break, if it is real.