Most players hit a wall at the same place: every easy technique is exhausted, no cell has a single obvious candidate, and the grid refuses to move. This is where pattern-based techniques earn their keep.
What an X-Wing actually is
An X-Wing is a rectangle. Find a candidate digit that appears in exactly two cells in each of two different rows, and where those cells sit in the same two columns. The four cells form the corners of a rectangle.
Because each row must contain that digit exactly once, the digit occupies one corner in each row — and whichever diagonal it takes, both columns end up covered. That means the digit cannot appear anywhere else in those two columns.
Spotting it quickly
- Scan one digit at a time, not one cell at a time.
- Look for rows where the digit has exactly two possible homes.
- Check whether two such rows share their column pair.
Swordfish: the same idea, one size up
A Swordfish is an X-Wing with three rows and three columns instead of two. The logic is identical, and so is the payoff: the digit is eliminated from those three columns everywhere outside the pattern.
When it is worth looking
Swordfish patterns are rare in puzzles below expert difficulty. If you are solving an easy grid and reaching for one, there is almost certainly a simpler move you have missed.
Practising deliberately
Techniques stick when you use them under mild pressure. Play a hard or evil grid, and when you stall, resist the hint button for two full minutes and scan digit by digit instead.