I always makes mistakes about this. I usually write Man rather than one. I think "man" is correct too. The translation depends on the speaker means.
If you say Man only has one life in English, that would be Människan har bara ett liv in Swedish.
If it were ’a man’ you’d have to have some article like en man or mannen, otherwise a noun cannot stand on its own like that, that’s how you know it’s a pronoun.
We'll accept this if Duolingo introduces a feature to "mark translation acceptable but don't show it otherwise". Until then, we'll wait. :)
With the previous sentence being about cats having nine lives, this sentence makes me feel slightly miserable.
It should also be mentioned that my cat is currently chilling on a nearby blanket giving me a smug look. As long as they have their blanket, that's about as far as feline compassion goes:)
In English that would be a very formal upper class way to say that.. It would be more usual to say " You only have one life ".
The translation with you is always accepted in cases like this (I hope). We know that the one with you is more natural, but we picked the one with one as a main translation because it's less ambiguous and makes it much easier when translating back into Swedish.
"Man lever bara en gång!" is a bit more natural and literally means yolo and is used like that. (I don't think I've heard anyone say man har bara ett liv)