Lesson
Black to move. Main line: 1... Bxe5 2. Bxe5 Qd5 3. f3 Qxe5
1...Bxe5! clears d6 and d5 with tempo. White’s bishop recaptures, but that places it directly on the queen’s new line.
After 2...Qd5, the queen attacks e5 and the exposed king-side structure. The quiet 3.f3 cannot save the bishop from 3...Qxe5.
A clearance move is about the square or line left behind. Before rejecting a sacrifice, inspect what the sacrificed piece was blocking for its own side.
To spot one, look for your own pieces standing on lines you would like to use, and ask what they would be worth if they left with tempo. A capture or a check buys the time that makes the clearance work.