Frame of reference

I had an opportunity to witness a portrait session. One object and five painters. Session lasted for almost 4 hours. All painters where out for cup of tea . With a breath of fresh air discussion begun on the their work. Meanwhile their teacher was examining the work and making notes.

Every one was called in and the notes were read out with the work. I was surprise to that the same object can be seen and perceived in the different way at the same time. Work produced was clear proof of it.

Teacher , then started comparing his work with student's work and to my surprise , one more perception was evident.

For me , many of the portraits were best piece of work but for the teacher all student's need to practice more to achieve perfection ,at the same time he was considering his work as a model. Naturally it was better than others.

After I compared teacher's work with poster by a professional photographer of the same subject it was way different.

So where the defect is ,

in expectation?
in perception ?
or in the frame of reference?

Technically teacher has all valid reasons to make that comments but for the me what pleases more is the best.

So do let me know if you workout how to achieve ZERO DEFECT here.