This is a big issue and one that most businesses are guilty of at some time. There are a number of reasons why businesses don't deliver on time. From my experience, the following are the main offenders.
First, in an attempt to keep the customer happy, the business will promise to deliver the product or service within a certain time. They know full well that they won't be able to deliver but are afraid that they will lose the sale if they admit they can't comply with the customer's delivery time frame.
Second, a disorganized business can often have poor ordering techniques that cause longer than expected delays in providing goods and services. All orders may go through once per week, so if you miss the ordering day you are a week behind from the start.
Third, suppliers may be unreliable and inconsistent. This is a common problem and one that is hard to deal with, especially as you may have to appease angry customers who don't really believe that it's not your fault.
All of the above happen every day. Customers do have high expectations in terms of delivery. Everyone wants everything yesterday. You may need to review your operation to ensure that these problems don't occur. Be honest with your customers and don't make promises that you can't keep. If you find that there is going to be a problem with supply, contact the customer to let them know. There is nothing worse than making a special visit to a business to pick-up your goods, only to find that they haven't arrived as promised.
Delivering on time is also very relevant for restaurants and professional services. People have a threshold and they don't like to be kept waiting. It's better to advise them of potential delays so that they can decide if they want to wait or not. Better to lose them this time around than to lose them forever because you kept them waiting for three hours. I have a doctor that I visit and his receptionist rings me prior to the appointment to let me know if he is running on time. This is a great service and it ensures that I don't sit in his waiting room for hours on end. The surgery is only a five-minute drive away, so I can keep working until I get the call that he will soon be available to see me. How many hours have you spent waiting in a doctor's or dentist's surgery?
Time is precious for all of us. Showing that you respect your customers' time is a very important way of distinguishing good service from lousy service.