The message came in at 9:14, while you were in the middle of a showing. You meant to answer it from the car. Then the next appointment ran long, and the one after that, and now it's night, the house is quiet, and that message is still sitting there, waiting for you.
Next to you is the notebook. Names, phone numbers, “call back Thursday,” “wants a yard for the dog,” half a page in Spanish and half in English. It knows more about your business than any software you've paid for, and it only works when it's in your hands.
And somewhere in those pages is the family who bought with you two years ago. Their home is worth more now, and they're ready to sell. They just haven't heard from you since the closing, and nothing reminded you to call.