I regularly visit a small shopping center which has numerous design issues, but one of them stands out. A busy side entrance has sliding doors which are attached to a motion sensor. The sensor itself is fine, but it’s positioned incorrectly. If you approach the door from an angle, nothing happens. The doors stay shut. If you walk backwards and attempt to trigger the sensor, still nothing. Only if you do a proper double take and walk directly towards the doors, open sesame.
Most shoppers who can’t get in, end up either using another door or wait until someone walks out so the the doors open. The cost for the user is minor stress and irritation. The cost for the business is having staff deal with someone who was just made feel stupid by a door. Stressful interactions lead to more sickdays.
However, some just turn away and go shop somewhere else. For those selected few, the cost of bad design is literal: they will spend their money elsewhere.