When faced with a difficult situation where information will create conflict, it is oh so tempting to remain silent, even though it takes much more energy to not be forthright. Whether you call it telling half-truths, witholding information, or lying by omission, anything short of true disclosure requires significant concentration on your part to keep it hidden.
Few people enjoy conflict and our ability as humans to avoid it is the stuff of legends. Yet, usually, as they say, the truth eventually comes out, compounding your situation with not only the original issue, but also now the fallout from the secret-keeping – hurt feelings. The sense of being betrayed. Or not-trusted. Anger toward you. It really is better just to be directly honest.
Really, I think most well-adjusted people already know this.
However, something that many people don't know is that the calmer you remain while sharing the information, they quieter the other person will also be.
We have in our brain mirror neurons – these cells cause us to mimic what we experience. Haven't you ever lost your voice and as you whisper, suddenly everyone around you whispers in return? (This is actually a fun trick to play on people – just start whispering and see if they can resist the temptation to make their voices much quieter). If you talk loudly, usually the other person does as well. If you insult them, expect to receive some slurs. If you exhibit signs of anxiety or fear, often, the other person will also experience these emotions. And, if you remain calm, they will too, or at least be much calmer than they would be if you had become agitated. If you speak with respect, generally, the other person will return the favor.
So, don't avoid that thing that needs to be spoken, but, by all means, do it calmly and with dignity. And let the truth set you free. It really does.