How to lose friends and alienate people

This essay is part of my thought process, not the end answer. 
I've always believed honesty to be the best answer. This has generally been a fairly easy mandate to follow. I know what is true, and what isn't. If I just tell the truth, the whole truth, and nothing but the truth, everyone would understand and it would all be OK.
Is it necessary to honestly convey what you feel? It now seems a bit elementary to me that I should be completely transparent. Its possible to be completely transparent and honest with feelings, and still paint a false or incomplete story. This honesty can result in unnecessary pain.
A couple nights ago, I told a good friend exactly how I felt about a part of our relationship. I didn't say one lie, nor did I exaggerate any of the details. Everything was said with the best of intentions, but I hurt my friend deeply. I wanted to help and improve the situation, but my brazen honesty somehow became selfish when I didn't consider how it would affect the other person and was only considering how I felt about the situation. We haven't spoken since.
No doubt time heals a lot of mistakes, but time also prevents mistakes from happening. Tact is a fundamental of any healthy and honest relationship. What if, instead of honestly conveying feeling at the time of their conception, I had waited a week to distill them into something tactful, beneficial, or maybe realize that the problem isn't worth worrying about at all. Is it dishonest to act differently than you feel until you sort your feelings out?
The solution might be in respect and trying to meet the needs of the other person over your own needs. Hmmm... more thoughts to come.