Wikipedia
In interpersonal communication, an I-message or I-statement is an assertion about the feelings, beliefs, values etc. of the person speaking, generally expressed as a sentence beginning with the word "I", and is contrasted with a "you-message" or "you-statement", which often begins with the word "you" and focuses on the person spoken to. Thomas Gordon coined the term "I message" in the 1960s while doing play therapy with children. He added the concept to his book for parents, P.E.T.: Parent Effectiveness Training (1970).
I-messages are often used with the intent to be assertive without putting the listener on the defensive. They are also used to take ownership for one's feelings rather than implying that they are caused by another person. An example of this would be to say: "I really am getting backed up on my work since I don't have the financial report yet," rather than: "you didn't finish the financial report on time!" (The latter is an example of a "you-statement").
I-messages or I-statements can also be used in constructive criticism. For instance, one might say, "I had to read that section of your paper three times before I understood it," rather than, "This section is worded in a really confusing way," or "You need to learn how to word a paper more clearly." The former comment leaves open the possibility that the fault lies with the giver of the criticism. According to the Conflict Resolution Network, I-statements are a dispute resolution conversation opener that can be used to state how one sees things and how one would like things to be, without using inflaming language