I walk to the door, open it, turn around and see someone behind me. They look up, see me holding the door open for them and immediately increase their pace to get to the door quicker.
This happens with the majority of people, they feel obliged to return the courtesy by lessening the time you spend holding the door.
Most of them also go on to say thank you as well. What separates the pro’s from the amateurs in this situation is if they start making small talk with you.
Then there’s the minority who don’t increase their pace, who don’t show gratitude and don’t make small talk. They test your resolve to hold the door open at all!
Thomas Duggan 