Why can't a lone cannon checkmate?
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 there is nothing to jump over. A cannon checks and captures only across exactly one screen, and a bare general in an empty palace provides none. So a lone cannon cannot even give check — it is not that mating is hard, it is that no check exists to build a mate from.
The fix is one piece
Keep a single advisor and the problem disappears: cannon and advisor beats a bare general, because your own advisor is a screen you control and can move into place. Cannon and soldier usually wins too, for the same reason, in 86.8% of positions.
This makes "do not trade your last advisor while your winning piece is a cannon" one of the most valuable rules in the endgame.
The defensive mirror
If you are defending against a cannon, your plan is to remove every possible screen — including your own elephants. Giving away an elephant for nothing can be correct, because against a lone cannon it turns a loss into a draw outright.
Related questions
Can two cannons mate?
Yes — each can screen for the other, which is the 重炮 pattern.
Cannon and elephant?
The elephant cannot cross the river, so it cannot reach the enemy palace to act as a screen there. Nor can an advisor, which never leaves its own palace: cannon and advisor wins because the cannon fires over its own advisor from home.
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