Lesson
White to move. Main line: 1. Rf7 Bd4 2. Kg3 Bg7
The bishop stays close to its king and simply refuses to be separated from it. There is no way to attack both at once, and the extra material never converts into a threat.
The defender does need to avoid one thing: being driven into the corner the bishop does not control, where mating nets exist. Keeping the king near the safe corner is the whole defensive idea.
The tablebase confirms the draw, and every move in the line above was checked to keep it. Recognising drawn material balances is a practical skill in its own right — it decides whether to trade into this ending or to avoid it.
Knowing what does not win is a skill
A rook is worth more than a bishop, and in this ending that is worth nothing at all. With the defending king near the corner the position is a theoretical draw, proven — not "probably holdable".
The value of knowing it is mostly decided before the ending appears. It tells you whether to trade into this position when you are the one down material, and whether to avoid it when you are up.
Why the defence holds
The bishop never leaves its king’s side, and a bishop defends itself at a distance along a diagonal, so the two are hard to separate. There is no way to attack both at once, and without that the extra exchange never turns into a threat.
The attacker’s only real try is to drive the king towards the corner the bishop does not control, where mating nets exist. Staying near the safe corner removes even that.
The defensive setup shown: Drawn. The defenders stay together and nothing can be attacked twice.
Letting the king be driven to the wrong corner: This is the one way to lose it — mating nets exist there, and only there.
Rook against bishop is a proven draw with the defenders together — press it and you are spending clock for nothing.
The bishop defends at a distance, which is why this defence is easier than the knight version.
The only real danger is the corner the bishop does not control.
Source: Syzygy endgame tablebases (via the Lichess tablebase API) — https://tablebase.lichess.ovh/standard