Lesson
White to move. Main line: 1. Rf5 Ne6 2. Kg3 Kg7
A knight separated from its king is in real danger: it moves slowly, it cannot lose a tempo, and a rook can take away its squares one at a time. Keeping it beside the king removes every one of those problems.
That is the difference from the bishop version. A bishop can defend itself from a distance along a diagonal; a knight has to be physically next to help, so the defence is more precise even though the verdict is the same.
Verified as a draw against the tablebase, with each move in the line checked to hold it. The practical lesson is the same as with the bishop: know which endings are drawn before you trade into them.
The same verdict, a harder defence
Rook against knight is drawn, like rook against bishop — but the defence takes more care, and it is lost in practice far more often. The difference is entirely about how the two minor pieces defend themselves.
A bishop can sit far from its king and still be safe along a diagonal. A knight has to be physically beside the king, because on its own it is slow, cannot lose a tempo, and can be cornered by a rook taking its squares one at a time.
What actually loses it
Almost every practical loss comes from the same mistake: the knight wanders. It goes to grab a square or block a check, the rook cuts it off from the king, and then it is trapped — not immediately, but inevitably.
The defensive rule is therefore blunt: keep the knight next to the king and move the king rather than the knight whenever there is a choice.
Keep the knight beside its king. Separated, it is the one minor piece a rook can actually trap.
Prefer king moves to knight moves when both are available — the knight’s position is the thing worth preserving.
The verdict is a draw, but unlike the bishop version it has to be defended accurately to stay one.
Source: Syzygy endgame tablebases (via the Lichess tablebase API) — https://tablebase.lichess.ovh/standard