If the flight is good with a couple of mistakes but the pilot is still elated as to be expected, you'll destroy the experience and their newly gained confidence.
Part of the skill of being an instructor is to engage with a student so they can recognise and openly discuss mistakes without destroying confidence.
then you drag them into a stuffy little room and pick them up on all the things they could have done better
You are either a potential fiction author or in need of a new flying school!