Im afraid Ive heard this story more times than I can count anyone who has been involved in rescue for long has heard it, too: Family wants to do the right thing and adopt a shelter or rescue dog; family waits for just the right dog to come along to the shelter/rescue; family is matched with/meets dog, falls in love; family takes dog home . . . and somewhere in the first week, or even the first DAY, the dog is inadvertently given an opportunity that the family, who has been filled with anticipation for weeks or months, just didnt expect the dog escapes and disappears. Was it a stop at the gas station on the way home, when little Billy got out of the car to use the restroom and left the car door open for a minute? When the family thought the dog would follow them into the house when they arrived home with the dog and just let her out of the car? When a visitor who came over to the house lingered too long in the doorway, without thinking to block the dog from slipping outside?
However it happens, losing the new dogs is usually a huge disappointment for the family, who has waited so long. But its often an even more wrenching disappointment for the group or person who fostered the dog; they may have invested weeks or years in saving and rehabilitating the dog, providing medical care (something as simple as spay/neuter, for example, or as lengthy and involved as treatment for demodex or heartworm), and perhaps helping the dog make a transition from being a neglected dog on a chain, to learning to live with and enjoy humans and fellow companion animals inside a home, with a family. To learn that a dog you invested money and time and love has gone poof! Just heartbreaking.
I fostered an obese and anxious Labrador a couple years ago; she had been surrendered by an older man who had gone into long-term care (without hope of recovery), and had never spent more than an hour without him in her three-year-old life. She liked people, and was very jolly and friendly with me, and seemed perfectly content to hang out with me, but her constant panting and tense ears belied the jolliness. Her tension was confirmed the first time I unclipped her leash and let her out the back door of my house unbeknownst to her, into a very securely fenced backyard; she ran like a demon was chasing her. Only when she discovered there was no way out no open gate, no low or rickety fence did she turn back toward me, smiling as if that little escape effort hadnt happened.
Who knows why dogs do this? Why cant she see that we love her and want to provide everything for her? Shes been so abused why cant she see what a nice home this will be for her?
But most dogs arent looking at every new person or place like an orphan who has been spoon-fed fantastic stories about how great her new life is going to be with her new family. All they know is that they have been taken away by strangers once again, and even if the strangers are very nice, this isnt home. The instinct for the dog to find something familiar (even if what was familiar for the dog was not so nice) is VERY STRONG.
I guess its understandable that people look at the whole thing from a human perspective, but you have to TRY see it from the dogs point of view; dogs havent been anticipating and visualizing their new lives with a new family the way the new family has been imagining how the dog is going to complete their lives. You have to keep the dog long enough to bond to you before you can trust him not to bolt at the earliest opportunity.