So they've been constantly injured, the butt of every joke and misfortune, much to the audience's amusement, and it seems the universe itself just likes screwing with them. So what's happening now? Huh... they're happy?
Yes, it seems that fate/God/the writers finally decided to Throw the Dog a Bone. It can be them ultimately coming out ahead, or just having a break for once, but it's generally very satisfying to whomever it happens to and any fans that had felt sorry for them.
One way this can happen is if the "Dog" character gets into a relationship. This can be very irritating to fans of the other character if it comes across as a reward and objectifies the love interest, especially if the "Dog" character is male and the love interest is female - in particularly bad versions of this; they might come across as - by this trope's very metaphor — a "bone." (Even "better", listen to fans complain if this doesn't happen.)
If the bone is thrown only to be cruelly snatched away later, then this becomes Yank the Dog's Chain, a set-up for the writers to further toy with the hapless character.
Compare Karmic Jackpot, Earn Your Happy Ending (the ending-specific variant of this trope) and Complimenting the Oddball. Contrast with Team Rocket Wins. If the character in-question happens to get this permanently and completely by chance, instead of temporarily, then it's Serendipity Shock.