As Hemingway said about writing, "You can leave out what you KNOW, but you can't leave out what you DON'T KNOW." Simple can be ignorant.
You have to do many miles of painting before you learn, eventually, what to leave OUT. This means that you have to develop your TASTE as you go along. You can be born with talent, but you have to DEVELOP it (by yourself and usually with some help). TASTE you have to develop by yourself with many years of practice. I disagree with instructors, in a way, who keep saying "paint simply." I know from personal experience I had to throw in everything INCLUDING THE KITCHEN SINK before I could discriminate between that which was really needed and that which needed to be dispensed with. Took a very long time.