There is a sense in which putting together a sermon is much like editing a movie. Just like much of what is shot for the movie is left in the computer or cutting room floor, so it is for a sermon. After prayer and study a preacher almost always has to leave out thoughts, insights, and information either because they do not fit the context of the sermon, or he just doesn't have room to fit them in.
There is also the preaching moment, which sometimes is editing on the fly, in which the preacher adds things he did not intend to say and had not thought about, or leaves out things he had intended to say, things that he considered important and necessary, things that were even in his notes or preaching manuscript.
In either of the above scenarios the preacher can always second guess himself, and get into the, "Oh, I could have said this...Oh, if only I would have said that... Oh, I should have said this...game with himself, and many of us do. Now, I am not saying the preacher should never examine his sermons or think critically about them, or that we should not get upset in those rare occurrences (and they should be rare) when we preach that uninspired and unaccompanied by the Spirit clunker of a sermon; BUT I am saying that at some point we have to trust the Lord with His superintending of the process of preparing the sermon and His superintending our preaching of the sermon. If we are working hard in the preparation and are praying for His illumination, His revelation, His guidance, His making His thoughts our thoughts and His words our words, then we must trust Him with what is left in the study and with what actually comes or doesn't come out of our mouth when we are delivering His word.
When we know that we have done the best we could, then we must trust the Lord that it was enough; and that just as the Lord took the fish and the loaves and fed the five thousand, He will take our meager thoughts and words and by His power multiply them to feed those to whom we preach.