A false metaphor is a gift to the devil; and the metaphor of choosing the right hill to die on is an example.
Behind the phrase is the idea that we are engaged in the kind of war where generals strive to locate their troops on the most advantageous ground for a decisive - win or lose - battle.
This analogy is then misapplied to the spiritual war of Good and evil by those who imagine that they are on the side of Good, to create the fake problem of choosing which 'issue' it will be most advantageous to 'make a stand' upon. Until that point, the assertion will repeatedly be made (whether explicitly or not) that this is not the hill I choose to die upon. Because?... the issue is too trivial, it is not decisive, my position is too weak, there is insufficient support etc.
So the person voluntarily retreats, quietly yields - or maybe complies with public wailing and hand-wringing - but complies; he will 'keep his powder dry' for the great and decisive conflict to come; when eventually he will reach that much-anticipated hill on which he will fight to the death...
But The Enemy is not seeking a final decisive conflict - but doing every-thing possible to avoid it; instead the enemy strategy is to encourage endless incremental yieldings of ground - until there are no more hills. Until victory has already been achieved. Every single decision not to fight on this hill materially aids the enemy strategy.
The metaphor is false, misleading, and plays directly into The Enemy's hands.
Adherence to Good is primary, therefore real resistance to evil is not like that.
How it really works is this: Each time ground is voluntarily yielded to evil, the position of Good is weakened, and The Enemy is strengthened.
The correct analogy is repentance (which means acknowledgment that sin is indeed sin, and rejection of it as an ideal).
The only repentance is repentance Now.
To say to oneself - I will repent later; to plan repentance - is Not to repent at all. It is, indeed, to render later (planned) repentance false, therefore impossible.
Either we repent now, or we have (as a matter of fact) rejected repentance. Either we resist now, and every-thing that is evil, or we have chosen to comply and joined-with Satan.
Every such failure, every chosen compliance, strengthens the enemy, and brings Them closer to Their goals.
Every yielding increases Their harvest of damned souls, because by it we are adding our-selves to the forces of evil.
Every untruth harms the cause of Good by joining our efforts with the Prince of Lies.
And vice versa... (so be hope-full)
Things really are That Simple.