You bring up an interesting point few seldom realize, that “voice” we all have in our head, the “inner critic”, is almost always negative. He never takes a day off. If you want to play this game to the best of your ability, you have to understand HOW to shut it up.
When you’re at the table, you don’t need to think. Many will argue that’s impossible as you have to make decisions about shot selection or safety from where the balls lay as you come to the table. It’s about coming to the understanding that you can do this without that voice.
Start “seeing” the various choices, then “see” what you want to do, in excruciating detail. The key is visualizing, not having a conversation in “words” with that voice about it. Your subconscious mind, the one that performs every physical action acts on images, pictures, video if you will, not on words. It takes some time and practice, you can do it away from the table as well in meditation. After a while you just learn to “see video clips” in your mind of your shot and safety options instead of a conversation.
Just show a clear picture to your subconscious with the conversation. It’s like a muscle that gets stronger when you utilize it. In time the voice recedes into the silence.