Intractable

/ɪnˈtræktəbəl/ adjective hard

So difficult to manage or resolve that ordinary efforts simply fail against it.

The negotiators faced an intractable dispute over water rights that had outlasted three previous treaties.

Memory Trick

'In-' (not) plus 'tractable' (able to be pulled or steered, like a tractor) — an intractable problem can't be steered into line.