fn(args, deps) Is Programming to Interfaces — And That's How You Control Nondeterminism

Many software systems fail for one very boring reason.

Not because of microservices. Not because of monoliths. Not because of whatever methodology war is trending this week.

They fail because they are unpredictable.

If you make a change and you cannot reliably determine the impact, you cannot safely evolve the system. And when you cannot evolve it, it starts behaving like legacy.

Determinism is the bridge between "works on my machine" and "works every time, everywhere."

fn(args, deps) gets you there — not because it is a clever trick, but because it makes boundaries explicit. Your logic programs to interfaces, which is what lets you control sources of nondeterminism.