Say the hard conversation out loud once before you have it. Words sound different outside your head.

Your own tone is invisible from the inside. In your head it all sounds reasonable; spoken aloud, you hear the sarcasm, the blame or the apology you never meant to include. That gap is why conversations go wrong when your intentions were good the whole way through. Hearing yourself is the only way to catch it in advance.

Record it on your phone and play it back once, which feels ridiculous and works. Listen for tone rather than content. Change the two words that come out harsher than you meant, then go and have the conversation while it is fresh.