Tactics
Interference
A rook defends a square along a file. Put something in the way, anything, and the defence is gone without the defender having moved at all. It is the rarest of the common tactics and the hardest to see, because the interfering piece is usually offered on a square where two enemy pieces can take it.
How to spot it
Look for enemy pieces defending each other along a long line with a gap in it. Then ask what you can put in the gap, and notice that both of the pieces that can capture it are busy: the moment either takes, it stops doing the job that made the position hold together.
The positions
Easiest first. Every one is from a real game, and the rating under each board is what it costs the players who have tried it on lichess.
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1. Black to play Play it out →Answer
19...Re5 20.Qc1 Rxc5
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2. Black to play Play it out →Answer
4...Bf6 5.Qg3 Bxa1
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3. Black to play Play it out →Answer
13...Qb4+ 14.Bd2 Qxd4 15.Nxc5 Qxc5
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4. White to play Play it out →Answer
27.Bc5 Qb8 28.Bxb4
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5. White to play Play it out →Answer
22.c4 Qd7 23.Nxe5 Qd4 24.Nxd3 Qa1+ 25.Qb1
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6. White to play Play it out →Answer
32.Bd6 f6 33.Rxd3
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7. Black to play Play it out →Answer
9...Bxc3 10.Bxc3 Be4 11.Qa6 Bxg2
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8. White to play Play it out →Answer
8.Be5 Qa3 9.Bxg7
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9. White to play Play it out →Answer
10.Qh5+ Kd7 11.Qxf5+ Ke7 12.Qf7#
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10. White to play Play it out →Answer
27.Qxg7+ Kxg7 28.Rxh7+ Kf8 29.Rh8+ Ke7 30.R1h7+ Kd6 31.Rxd8+ Kc5 32.Rxd4
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11. White to play Play it out →Answer
28.Qg8+ Nf8 29.Re2 Qd4+ 30.Kxg2
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12. White to play Play it out →Answer
25.Rxa6+ Ke8 26.Rxa8+ Qd8 27.Rdxd8#
Reading about a pattern is the easy half. Motify finds the positions where you missed one, by running your own lichess and Chess.com games through Stockfish, and puts each of them behind two or three puzzles on the same idea so you meet it having just found it three times. See how Motify works.
Positions from the lichess puzzle database, released under CC0.