Why does a lone attacking piece rarely checkmate the general?
These answers restate the rules implemented by our open-source engine, which follows the WXF laws for movement, checkmate and both repetition rulings: a side that forces a repetition by perpetual check or perpetual chase loses rather than drawing. The chase half has not been validated against the official casebook. Where an answer refers to a specific position, that position lives on the linked reference page, where the build verifies it before publishing.
Direct answer
Because the general itself defends its own adjacent points, and advisors typically defend more, so a single attacking piece usually cannot cover every escape square at the same time. Checkmate almost always needs at least two coordinated attackers, and your own general counts as one, or one attacker working with a favourable palace structure the defence has already weakened.
The arithmetic of it
A general in the centre of the palace has up to four adjacent points, and the flying-general file besides. Covering all of those with one piece simultaneously is rare; most single-piece checks simply push the general to an adjacent safe point instead of ending the game.
The exceptions that do work alone
A single piece can mate unaided when the defender's own pieces have already sealed off the escape points, most notably a smothered general, or when the general has been driven to a corner with only one or two points left to defend at all. These are the situations basic checkmate patterns are built around.
The biggest exception is the bare general. Once the defender has nothing left, your own general becomes the second attacker: it takes away the enemy general's file under the flying-general rule, and a lone chariot, a lone horse, or even a lone soldier that has not yet reached the last rank then forces mate. The lone cannon is the one piece that cannot, because it has nothing to jump. See the proven endgame verdicts.
Related questions
Does a chariot alone ever checkmate quickly?
Yes, because it can cover an entire rank or file's worth of points at once, which is why chariot mates are the fastest of the basic patterns.
Is a lone cannon check ever mate?
Very rarely, and never against a bare general, since a lone cannon in an empty palace has nothing to jump over at all.
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