I quite like the phrase ‘needs-must’ as a way to say ‘doing what need imposes upon you’. What I only just learnt about it was that it comes from a longer phrase.
The full modern phrase is ‘needs must when the devil drives’, and that comes from a very early (1400s) phrase ‘he must needs go that the devil drives’.
It essentially means if the devil drives you, you have no choice but to go which is still interpreted similarly to needs-must, but I wonder what it meant to the people of the 1400s. Maybe it did mean the same, but it’s interesting that there’s no sense of being able to resist the devil. Well, maybe it was a vulgar phrase that the church didn’t approve of!