의미: 그냥 하던 일이나 잘해라!
This phrase is usually used when someone does something new (like singing, playing an instrument or basically anything) and does it badly.
It means that they aren't good enough at what they are doing to quit their normal or "day job" to support themselves doing this new thing.
So, it's definitely NOT a complement!
연관표현: Don't give up the day job.