A difficult conversation delayed long enough becomes several difficult conversations.

A postponed difficult conversation grows additional subjects. Now there is the original issue, the fact that you did not raise it, the resentment that built while you waited, and whatever happened in the interval because it was never addressed. One conversation becomes four, and the four are harder than the one.

If something needs saying, aim to say it within days rather than months. Keep it to the original subject if you can. And if it has already grown, name the accumulation honestly rather than trying to have all of it as a single conversation.