be onto a good thing
be on to a good thing
To be in a favorable job, position, or situation that has the potential to become very advantageous, lucrative, useful, etc., in the future. A: "Because I can work from home, I can look after the kids when my wife goes to work." B: "Wow, you're really on to a good thing here! Your new boyfriend seems really sweet—I think you two are on to a good thing.