Difficult conversations often fail not because of the topic, but because of pace, tone, and timing. Speak in I-statements instead of accusations. Formulate one concrete wish instead of a full reckoning. If you notice that you only want to prove a point, take a break. A good opening is often: I want to bring something up without us turning against each other.
Starting again after an argument
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What helps after conflict when you do not want to pretend nothing happened.