They have a great mental model of the inner workings on the product. Even for a part of a code they haven't seen in a long time. When you debug code with such a

They have a great mental model of the inner workings on the product. Even for a part of a code they haven't seen in a long time. When you debug code with such a person, you notice that they seamlessly translate the piece of code on the screen to the mental model and back (it probably takes hours for Jr engineers to piece those together). Neo deciphering the matrix is a good analogy.