I spent around thirty years in management, ownership and leadership before this work. A great deal of that was difficult conversations: with staff, with customers, with people who were upset and not always reasonable about it.
What I learned is that the difficulty is almost never the conversation itself. It is what you have built up around it while avoiding it.
Why you keep not having it
Usually one of three things.
You have rehearsed the worst version. Every time you imagine it, you imagine it going badly, so your brain files it as dangerous. By month four you are not avoiding a conversation, you are avoiding a disaster that has never happened.
You are trying to say several things at once. The thing you want to say has grown. It now contains six examples, three old grievances and an apology for bringing it up. Of course you cannot start.
You are waiting for a good moment. There is no good moment. That is what the waiting is for.
The conversation is not the hard part. Carrying it around unsaid for a year is the hard part.
What actually works
Work out the one sentence
Not the speech. One sentence, under fifteen words, that says the actual thing. If you cannot get it that short, you have not found it yet. Keep cutting until what is left is true and uncomfortable. That is the sentence.
Say it in the first thirty seconds
Most people bury the real point at the end, after a long run up. By then the other person has already decided what the conversation is about and is defending themselves against the wrong thing. Lead with it.
Separate the thing from the person
There is an enormous difference between what you did on Tuesday did not work for me and you are inconsiderate. The first is a conversation. The second is a fight.
Decide what you want before you start
An apology, a change, or just to be heard. These are three completely different conversations and most people start without knowing which one they are having.
Let the silence happen
After you say your sentence, stop. Do not fill the gap with softening. The silence is where the other person processes, and most people wreck their own point by talking through it.
If it goes badly
Sometimes it does. You said the true thing and they reacted badly. That is information too, and it is better information than another year of not knowing.
What I have almost never seen is somebody who regretted having the conversation. I have seen hundreds of people who regretted the years they spent not having it.