1. Don’t sugar coat or downplay what happened - this leaves room for more positive interpretations and conclusions than are warranted. It’s misleading and once the person discovers what you really meant, trust is harmed. It results in confusion about where you stand and what you expect. It is dishonest, ineffective, and interferes with timely performance management.
3. Don't resort to corporate speak - this creates a distance between you and others, and it's generally perceived as inauthentic. It portrays you as disconnected, as if operating from an ivory tower. Corporate speak can be interpreted as an attempt to abdicate responsibility with an air of blaming and hiding.
4. Don't solely focus on emotions - this can feed into escalations and direct attention away from critical thinking and problem solving. If you focus on emotions too strongly you may needlessly emphasize personal sensitivities and interpersonal dislikes. This hampers logic and crisis management. Emotions absolutely need to be acknowledged and taken into account, just be careful when to attend to them and in what manner. Know when to focus on facts, when on emotions.
5. Don't use overly positive phrases such as "We are really lucky to be handed this learning opportunity" or vague phrases such as "A mistake was made" - this too creates confusion and communicates a lack of accountability. Such phrases are generally not credible thereby eroding trust and engagement. Instead, be clear: "We delivered this project passed the deadline because we misjudged the length it would take to accomplish step 3 and 4. We will now take the following action ..."
Say it as it is, pretty or not. Do it respectfully and expect the person to find it difficult to deal with such candor. For more information on this topic: