Do 'de' and 'det' sound identical? If so how do you know which is wanted here? 'De' wasn't accepted but makes equal sense.
Does this sentence mean like (Eat your spinach), it's good for you? Or does it mean like congratulations - Good for you!? How would a Dane use this sentence?
Strictly speaking it could mean both but it is almost always used in the 'spinach' sense.
For congratulations i would simply say "godt" if you got lucky, or "godt gået" if it was a result of your own effort.
Why is "this is good for you" wrong? How do I differentiate between this and that in Danish?