Going for really hard shots are the same as going for low percentage shots. You will miss much more than you make them. This causes you to lose confidence. When you see the pros "come with the shot"- which is when they execute a very difficult shot, it's because they have spent countless hours practicing shots like that.
As for quiet eyes, I know what you are talking about now. They did a study about sports that require hand-eye coordination, and the people who have less eye movement, and stare at spots longer play better. This applies to pool, and I am glad you reminded me of it (because I forgot to practice this), but I don't agree that you should look at the cueball only once. You have to look at the cueball because of tip placement. Then you take your practice strokes, your eyes look back and forth. Just looking at your tip placement, and then doing a few practice strokes without looking at the cueball again, that's like shooting blind. Your tip can stray just a fraction of an inch and it will change to whole outcome of the shot.
Pay close attention to videos of the pros. Every single one of them looks back and forth a few times on every shot. I have never seen someone look at the cueball only once. It doesn't make any sense to do that.