He'll be extremely nonchalant or recklessly determined (4-4)

I believe the answer is:

hell-bent

I'm a little stuck... Click here to teach me more about this clue!

But I can't explain it at all! Could you help me understand?

(Other definitions for hell-bent that I've seen before include "Determined at all costs" , "Dogged - persistent" , "Absolutely determined" , "Recklessly determined" , "Dead set" .)

I've seen this clue in the Sydney Morning Herald.

Want a hint initially instead of a full solution? Install my app