Mark is an abstract data type, because it must be between 0 and 100. Date is an abstract data type. Time is abstract data type. Person is the most abstract data type ever. It contains all the abstract data type it wants to hold.
To me, one can never truly understand another without being with them 24/7. A person can be surprising at any time. They can act out of norm because they are also human beings. That's what human beings do. Decide on whatever basis they want to. Either others' suggestion, or they own discretion and judgment, it is still our own decision.
What we choose to be, how to react, and what relationship are we having. These are just a few of countless abstract data type we are dealing on a daily basis. Today, we might decide to do this, but tomorrow, it might be the total opposite.
We also choose to be ignorant, responsive, up to date, and hyperactive. We choose what people will see in ourselves. Don't we just abstract?