There was an occasion, when I was a young graduate just starting work in 1995, I received an email containing a project plan from my project lead. I just assumed that the project plan was from our boss and felt that the project plan is very unrealistic. Unhappy about it but unsure how to go about it I expressed my dissatisfaction to my project lead saying that our boss is disconnected from our work. With a shocked expression, my project lead told me that the project plan was from him not the boss! I had essentially told my project lead that I think he is disconnected from the project and his plan is unrealistic!
At another job, I responded to an email where I was asked my opinion how best to deal with a specific situation and unfortunately my response in that email kinda indicate that another colleague has not been as detail in her work as she could have. She was subsequently added into the email thread where what I wrote was available to her. Like the above case, I ended up telling the person what I think in a manner that I would not have had I expressed my opinion or responded to what I was asked in the presence of or directly to the person involved.
What I have learned from these and other similar incidences is that always say/write as thought what you say/write is going to be made public or at least to the people concerned. If you have to say something concerning someone, say it in a way where you would say it directly to that person even if that person is not present at the time.
Taking this a step further, at Intel, we were all expected to make decision and act in a manner such that we expect our decision and action will be made public! In other words, if we are in the position where we have a choice, we are expected to make a decision thinking that our action will be made public. The thought that everything we do is transparent help guide us in our action. You will not dare do anything illegal or unethical or is against company policy etc.