I’m not sure which part made you feel that way. What Pressfield meant is that amateurs — those who are inexperienced and just starting out — feel that their art is representative of them. They feel paralysed as a result, and are afraid of making mistakes. It’s a problem because this fear holds them back from growth and doing creative work.
On the other hand, the seasoned professional is able to separate himself from his work. He’s not afraid of criticism or how imperfect his work is. He just puts time in to master his craft.
This is something that resonates with me, and hence I included his quote. You may disagree with me on this, and I would be happy to hear you out. But it’s not a knock on amateurs by any means.