How do I find a sacrifice that actually works?
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
Work backward from the mate, not forward from the piece you want to give up. A sound sacrifice starts with a mating pattern, or at least a decisive material gain, that you can see clearly, and only then asks what has to be removed to reach it. Sacrifices found the other way round are usually just hopeful guesses.
Start with the target, not the piece
Ask what would happen if a specific advisor, or the screen in front of an enemy cannon, simply were not there. If the answer is a forced mate or a clearly winning attack, you have found your sacrifice; the piece you give up is whatever removes that specific obstacle. This is the same logic behind every sound sacrifice, not just this one.
Check the opponent's best defence, not their worst
A sacrifice that only works if the opponent replies badly is not sound. Before committing, find their most stubborn response and confirm the attack still gets through. If it does not, the material was simply given away.
Related questions
Is a soldier sacrifice safer than a piece sacrifice?
Generally, since less is at stake if the calculation is wrong, but it still needs the same concrete justification.
What if I cannot calculate to the end?
Then it is a speculative sacrifice rather than a sound one. Those are sometimes still worth playing under time pressure, but know the difference.
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