"専門家とは非常に狭い分野で起こり得るすべての失敗をした人のことです。"

Simplified Meaning:

To become highly skilled in any area, you must learn from many mistakes. Imagine a chef who's excellent at making cakes. They didn't just wake up one day and know how to bake perfectly; they probably burned a lot of cakes, used too much flour, or forgot the eggs at some point. Each error taught them something valuable until they mastered cake baking. This idea can be applied to anything in life. If you want to be really good at playing guitar, for example, you'll hit the wrong notes many times. Each time you correct a mistake, you understand a little better how to play correctly. Over time, making and then fixing these mistakes is what turning you into an expert. So, don't be afraid of messing up. Each mistake you make is just a step towards becoming really good at what you do. Embrace those mistakes and learn from them. That's how experts are made.