It's not wrong, it's just contextless. のだから is generally a conector between the two sentences, but in this case the second sentence (the thing being explained) is implied in context. For example consider this possible conversation:
「なんでそんなに汗びっしょりなの?」 "Why is/are [pronoun] so sweaty?" (this sentence can be talking about you, he, she, it, they, depending on context)
「1日中テニスをしていたんだから。」"(Because) [pronoun] was playing tennis all day"
Here I shortened のだから into んだから, because that's a more conversational form (it's still the same thing).
When you see だから or other particles at the end of a sentence that is being treated as complete, that means the rest of the sentence is already clear in context or the person wants you to infer.
Thank you!
about のだから
Are the example sentences wrong?Looks like the example sentence in English doesn't contain the meaning of のだから.If wrong,than which sentence is wrong?The Japanese sentence or the English sentence?Or both?