There's an adage that says, "Honesty is not only the first step toward greatness, it is greatness itself." the implication being that being honesty is a life-long process. This adage is wrong. It is impossible always being honest to others including our friends.
There are circumstances when we would better not being honest when we give priority to others' feelings. For example, what will you do if your friend comes to you with excitement and asks for your opinion on his or her new hair-cut? Will you say "It sucks!" with no doubt? Absolutely not! To be a thoughtful friend, you would be well-advised to give some complements so that you don't ruin your friend's good mood.
Meanwhile, friends sometimes share secrets to each other, but when it comes to some personal matters which we want to keep in our heart, it is better not to tell the truth or it may spread out. Once at a party, some of my friends and I came together to play the game "truth or dare", it came my turn and I chose "truth", however I wasn't expected to be asked "who I am having a secret crush on ", which by no means I would never tell. I doubted for a second and answered "Nobody." Although I told a lie, I think it was for me to do that, as it is a secret I want to keep and there's nothing wrong with telling a lie in this particular circumstance. Similarly, everyone has some private matters which cannot tell anyone. So we should keep a certain distance in relationship even though among your closest friends.
I admit that there's no better way to be honest and sincere with people than to be a really considerate friend when your friend needs to know the truth in order to make an important decision. To be a bona fide friend, we are supposed to give our friends our real opinions, so that we can be reliable to them. Even so, it is wise to take the situation , which differs form time to time, into consideration first before we intend to tell the truth.
All in all, it is impossible to be honest with friends all the time. I believe in that because there are some circumstances that it is better for us to tell a lie in order to not hurt others' feelings, and keep our secrets and etc.