My first "failure" was my Sammy.
He was supposed to be here for a week that turned into 3. Fortunately (I mean that), the person never did come back. My latest is my Toby. I found him wandering around my complex, probably within an hour of being abandoned as he was still very clean (he has white paws). I was trying to find him a home, but he makes Tweety so happy that, yes I "failed."