Some time ago, my very wise bonvivant friend Rommel taught me a simple rule. I have been applying it, and have found it to be incredibly useful. Here it is:
If you have to say something to someone that you think will agitate them or hurt their feelings, do NOT say it in email or a text message. Speak to them on the phone or say it in person.
Rommel, being the eminently practical guy that he is, didn't speculate about why this was so. So I'll step up. First of all, there is the obvious fact that you don't have the option of using vocal inflection to soften the blow when you are writing. There is also the permanence of writing: someone once described writing as "words that stay", and this makes it harder for the hearer of the bad news to remember that the words are only your opinion, not immutable fact. But finally, there is the fact that when you give bad news or criticism in person or on the phone, you are PRESENT to the impact of your words in a way that you are not when you have expressed yourself in writing. In that way, you can take more responsibility for them. When you are present when speaking critically, you are vulnerable to the reaction from the other person, which is, of course, the danger, but your willingness to be present in this way can go a long way toward reminding the other person that you speak as a well-wisher or a friend, someone who is in the trenches with them in whatever they are attempting to do, and not a distant, evaluating onlooker.
I've been trying to practice it, and I have found that when I do, I like the results that I get. So I wanted to pass it on.